Conjectures with Functions & Relations
Classify the Function Type
Sort each function into the correct column: Linear, Quadratic, or Exponential.
Function Type to General Form
Draw a line from each function type to its general form.
Linear, Quadratic, or Exponential Table?
Look at the pattern in each table of values. Circle the correct function type.
x: 0, 1, 2, 3, 4 → y: 3, 5, 7, 9, 11 (constant first difference of +2)
x: 0, 1, 2, 3, 4 → y: 1, 4, 9, 16, 25 (first differences: 3, 5, 7, 9 — constant second difference of +2)
x: 0, 1, 2, 3, 4 → y: 2, 6, 18, 54, 162 (each value is ×3)
x: 0, 1, 2, 3, 4 → y: 0, 1, 4, 9, 16 (first differences: 1, 3, 5, 7 — constant second difference of +2)
Identify the y-intercept
Circle the y-intercept (the value of y when x = 0) for each function.
y = 2x + 7
y = x² − 3x + 5
y = 4 × 2ˣ
y = (x − 2)(x + 3)
y = −3x² + 12
Graph Shape to Function Type
Draw a line from each graph description to the function type that produces it.
Identify the Gradient
For each linear function, circle the gradient (slope).
y = 5x − 3
y = −2x + 8
2y = 6x + 10 (rewrite as y = 3x + 5)
y = ¾x − 1
Function or Not-a-Function?
Sort each relation: Function or Not a Function. (A function assigns exactly one y-value to each x-value.)
Evaluate Functions
Circle the correct value of each function at the given x-value.
f(x) = 2x − 3; find f(4)
g(x) = x² + 1; find g(−3)
h(x) = 3 × 2ˣ; find h(3)
f(x) = (x − 1)(x + 5); find f(0)
g(x) = −x² + 4x; find g(2)
True or False — Quadratic Conjectures
Circle TRUE or FALSE for each conjecture about quadratic functions.
All quadratic functions have exactly two x-intercepts
The graph of y = ax² + bx + c is always a parabola
If a > 0 in y = ax² + bx + c, the parabola opens upward
The vertex of y = x² + bx + c is always on the y-axis
A quadratic function can have at most one axis of symmetry
True or False — Exponential Conjectures
Circle TRUE or FALSE for each conjecture about exponential functions.
The graph of y = aˣ (where a > 1) always passes through (0, 1)
An exponential function can produce negative y-values when a > 0
The graph of y = 2ˣ has a horizontal asymptote at y = 0
Exponential decay (0 < b < 1) means y eventually becomes negative
Multiplying by a constant (e.g. y = 5 × 2ˣ) changes the y-intercept but not the growth rate
True or False — Linear Conjectures
Circle TRUE or FALSE for each conjecture about linear functions.
A linear function can have a maximum or minimum value
If two linear functions have the same gradient, they never intersect (assuming different y-intercepts)
A horizontal line (y = c) is a linear function with gradient 0
Every straight line can be written in the form y = mx + c
The gradient of a linear function tells you the rate of change of y with respect to x
Transformation to Effect on Graph
Draw a line from each transformation to its effect on the graph of y = x².
Find the Vertex
Circle the correct vertex (turning point) for each quadratic in turning point form y = a(x − h)² + k, where vertex = (h, k).
y = (x − 3)² + 2
y = −(x + 1)² + 7
y = 2(x − 5)² − 4
y = −3(x + 2)²
Axis of Symmetry
The axis of symmetry of y = ax² + bx + c is x = −b/(2a). Circle the correct axis of symmetry.
y = x² − 6x + 8 (a = 1, b = −6)
y = 2x² + 8x + 1 (a = 2, b = 8)
y = −x² + 4x − 3 (a = −1, b = 4)
y = 3x² − 12x + 7 (a = 3, b = −12)
Steps to Find the Vertex of y = x² + 4x − 5
Put the steps in the correct order to find the vertex of the parabola y = x² + 4x − 5.
Number of x-intercepts from the Discriminant
The discriminant is Δ = b² − 4ac. If Δ > 0: two x-intercepts. If Δ = 0: one x-intercept. If Δ < 0: no x-intercepts. Circle the correct number.
y = x² − 4x + 3 → Δ = (−4)² − 4(1)(3) = 16 − 12 = 4
y = x² + 6x + 9 → Δ = 6² − 4(1)(9) = 36 − 36 = 0
y = 2x² + x + 3 → Δ = 1² − 4(2)(3) = 1 − 24 = −23
y = x² − 5x + 2 → Δ = (−5)² − 4(1)(2) = 25 − 8 = 17
Discriminant Value to Number of Solutions
Sort each discriminant result into the correct column.
Parabola Opens Up or Down?
Sort each quadratic function: Opens Upward (a > 0) or Opens Downward (a < 0).
Investigate: Coefficient of x² and Parabola Width
Investigate the following conjecture. Show your reasoning with examples.
Conjecture: 'When you increase the coefficient of x² in y = ax², the parabola gets narrower.' Test this by comparing y = x², y = 2x², y = 5x², and y = ½x². For each, calculate y when x = 1, 2, and 3. What happens to the y-values as 'a' increases? Explain why a larger 'a' makes the parabola narrower.
Investigate: When Does Exponential Overtake Linear?
Test the conjecture and show your working.
Conjecture: 'An exponential function will always eventually exceed a linear function.' Test with y = 2ˣ and y = 100x. Calculate both functions for x = 0, 1, 2, 5, 7, 8, 10, and 15. For what values of x is the linear function greater? At approximately what x-value does the exponential overtake? Explain why this must always happen eventually.
Find and Verify x-intercepts
Find the x-intercepts of each quadratic and verify your answer.
Find the x-intercepts of y = x² − 2x − 15 by factorising. Then verify by substituting each x-intercept back into the equation. Also find the vertex and sketch a rough graph labelling the intercepts and vertex.
Find the x-intercepts of y = 2x² + 5x − 3 by factorising or using the quadratic formula. Verify your solutions. How does the discriminant confirm the number of intercepts?
Compare Two Functions for Same Output
Find where two functions produce the same y-value.
For what value(s) of x do f(x) = x² − 3 and g(x) = 2x + 1 give the same output? Set them equal and solve: x² − 3 = 2x + 1. Verify your solutions by substituting into both functions. What does this represent graphically?
A linear function f(x) = 50 + 10x and a quadratic function g(x) = x² model two different situations. Find where they intersect. For what x-values is the linear function greater? When does the quadratic overtake?
Investigate Translations
Explore how translations affect a function's graph.
Starting with y = x², investigate what happens when you replace x with (x − h). Compare y = x², y = (x − 3)², and y = (x + 2)². For each, find the vertex and y-intercept. State your conjecture about how the value of h affects the graph's position.
Starting with y = x², investigate what happens when you add k. Compare y = x², y = x² + 4, and y = x² − 3. For each, find the vertex. Then combine both: describe the graph of y = (x − 1)² + 6 without plotting it.
True or False — Domain and Range
Circle TRUE or FALSE for each statement about function domains and ranges.
The domain of y = x² is all real numbers
The range of y = x² is y ≥ 0
The domain of y = 2ˣ is x ≥ 0 only
The range of y = −x² + 5 is y ≤ 5
The range of y = 3ˣ includes negative numbers
The range of a linear function y = mx + c (where m ≠ 0) is all real numbers
Create a Conjecture and Test It
Make your own conjecture about functions and test it systematically.
Create a conjecture about the relationship between the sign of 'a' and the direction a parabola opens, AND the number of x-intercepts based on the vertex's position. For example: 'If a > 0 and the vertex is below the x-axis, then...' State your conjecture clearly, test it with at least 3 specific quadratics, and explain whether your conjecture holds or needs revision.
Real-World Function Modelling
Apply function knowledge to a real-world scenario.
A cricket ball is hit into the air. Its height (in metres) after t seconds is modelled by h(t) = −5t² + 20t + 1.5. Find: (a) the initial height when hit, (b) the maximum height and when it occurs, (c) when the ball returns to ground level (h = 0). Explain what each part of the equation represents in context.
A company's profit (in thousands of dollars) is modelled by P(x) = −2x² + 24x − 40, where x is the price of the product in dollars. Find the price that maximises profit, the maximum profit, and the price range where the company makes a positive profit. What does the vertex represent in this context?
Graphing with Technology
Use a graphing tool (such as Desmos, GeoGebra, or a graphing calculator) to explore functions.
- 1Graph y = ax² for a = −3, −1, −0.5, 0.5, 1, 3. Make a conjecture about how the value of 'a' affects the parabola's shape and direction. Test with one more value of 'a' to verify.
- 2Graph y = (x − h)² + k for different values of h and k. Explain how to move a parabola to any position on the coordinate plane.
- 3Graph y = 2ˣ, y = 3ˣ, and y = 10ˣ on the same axes. Also graph y = 0.5ˣ and y = 0.1ˣ. Make a conjecture about how the base affects the steepness and whether the function grows or decays.
Real-World Data and Function Fitting
Collect or research real data and decide which type of function best models it.
- 1Collect data on the temperature at different times of day (e.g. 6 am, 9 am, 12 pm, 3 pm, 6 pm, 9 pm). Plot the points. Does the pattern look linear, quadratic, or something else? Justify your choice.
- 2Research Australia's population over the last 50 years (e.g. every 10 years). Plot the data. Test whether a linear or exponential model fits better by comparing predictions.
- 3Drop a ball from different heights and measure the bounce height. Plot drop height vs bounce height. Is the relationship linear? Find an approximate equation for the line of best fit.
Quadratic Functions — Key Features
Identify and explain all key features of a quadratic function.
For f(x) = x² − 6x + 8: (a) Find x-intercepts by factoring. (b) Find y-intercept. (c) Find the axis of symmetry. (d) Find the vertex. (e) State the minimum value.
For g(x) = −2x² + 8x − 6: (a) State whether parabola opens up or down. (b) Find axis of symmetry. (c) Find vertex. (d) Find x-intercepts. (e) State maximum value.
Function Vocabulary
Draw a line from each function term to its correct definition.
Parabola Features — Identify from Equation
Circle the correct answer for each feature.
f(x) = 3(x − 2)² + 5 — vertex is at:
f(x) = −(x + 3)² + 7 — the parabola:
f(x) = 2x² − 4x + 1 — axis of symmetry is:
f(x) = x² + 6x + 9 — discriminant is:
Function vs Not a Function
Sort each relation: Function or Not a Function.
The Discriminant — Nature of Roots
Use the discriminant to determine the nature of roots without solving.
For each quadratic, calculate b² − 4ac and state whether there are 0, 1, or 2 real roots: (a) x² + 5x + 6 = 0 (b) x² + 4x + 4 = 0 (c) x² + x + 3 = 0 (d) 2x² − 3x − 5 = 0
Steps for Solving a Quadratic by Factoring
Put the steps in the correct order.
Quadratic Formula
Apply the quadratic formula to solve equations that do not factorise easily.
Solve using the quadratic formula: 2x² − 5x − 3 = 0. State the values of a, b, c. Calculate the discriminant. Find both solutions. Verify by substitution.
Solve: x² + 3x − 1 = 0. Express solutions in surd form and as decimals correct to 2 decimal places.
Quadratic Roots to Equation Form
Draw a line from each pair of roots to the factored form of the quadratic.
Completing the Square
Use completing the square to rewrite quadratics in vertex form.
Rewrite f(x) = x² − 8x + 5 in the form (x − h)² + k by completing the square. State the vertex and axis of symmetry.
Rewrite f(x) = 2x² + 12x + 7 in vertex form. (Hint: first factor out 2 from the x² and x terms.) State the vertex.
Transformations of Parabolas
Circle the correct description of each transformation.
y = x² shifted to y = x² + 3 means:
y = x² shifted to y = (x − 4)² means:
y = x² changed to y = −x² means:
y = x² changed to y = 3x² means:
Conjectures in Algebra — Testing and Proving
Formulate, test, and attempt to prove algebraic conjectures.
Conjecture: 'The sum of any two consecutive integers is always odd.' Test with 3 examples. Then prove it algebraically using n and n+1.
Conjecture: 'The product of any two consecutive even integers is divisible by 8.' Test with 3 examples. Prove algebraically using 2n and 2(n+1).
Functions in Context — Projectile Motion
Apply quadratic functions to model projectile motion.
A ball is thrown upward from a height of 2 m with height h(t) = −5t² + 20t + 2 (h in metres, t in seconds). (a) What is the initial height? (b) Find the maximum height and when it occurs. (c) When does the ball hit the ground? (Solve h(t) = 0) (d) What is the height after 3 seconds?
Classify the Relationship — Function Type
Sort each context into the type of function that models it best.
Quadratic Functions — Real World
Find quadratic functions in real-world settings.
- 1Throw a ball straight up and catch it. Measure the time in the air. Using h = −5t² + vt, estimate the initial velocity v. What is the maximum height reached?
- 2Research the path of a basketball free throw. Estimate the launch angle and initial speed. Sketch the parabolic path and identify the vertex.
- 3Find a bridge arch or architectural arch. Measure or estimate its dimensions and write a quadratic equation that models the arch.
Polynomial Degree and End Behaviour
Analyse the end behaviour of polynomial functions.
For f(x) = x³ − 3x² + 2x: (a) What is the degree? (b) As x → +∞, what does f(x) do? (c) As x → −∞, what does f(x) do? (d) Find x-intercepts by factoring.
Compare the end behaviour of y = x² and y = x³. Explain why even-degree polynomials have 'matching' ends while odd-degree polynomials have 'opposite' ends.
Types of Quadratic Solutions
Tally the type of solution found for each quadratic in a set of 25 problems.
| Item | Tally | Total |
|---|---|---|
Two distinct real roots | ||
One repeated root | ||
No real roots (complex) |
Inverse Functions — Introduction
Explore the concept of inverse functions.
For f(x) = 2x + 3: (a) Find f⁻¹(x) by swapping x and y and solving for y. (b) Verify that f(f⁻¹(x)) = x and f⁻¹(f(x)) = x. (c) What is the graphical relationship between f and f⁻¹?
Explain why f(x) = x² (for all real x) does not have an inverse function, but f(x) = x² for x ≥ 0 does. What is the inverse of the restricted version?
Identify the Function from Its Graph Description
Circle the function type that matches each description.
A U-shaped curve with vertex at the origin, symmetrical about the y-axis
A curve that passes through (0,1) and increases very steeply as x increases
A straight line with negative gradient, crossing both axes
A curve shaped like an upside-down U, with a maximum turning point
Conjecture About Even and Odd Functions
Investigate symmetry properties of functions.
Define what it means for a function to be 'even'. Give two examples.
Define what it means for a function to be 'odd'. Give two examples.
Is f(x) = x² + 3 even, odd, or neither? Justify using algebra.
Is f(x) = x³ − x even, odd, or neither? Show working.
Match Function to Its Graph Feature
Draw a line from each function to the graph feature that best describes it.
Classify Functions by Type
Sort each function into the correct category: Linear, Quadratic, Exponential, or Other.
Investigating Translations of Parabolas
Explore how changing constants shifts the graph of y = x².
Describe how the graph of y = x² + k differs from y = x² for positive k.
Describe how y = (x − h)² differs from y = x².
Write the equation of a parabola with vertex at (3, −2) and opening upward.
Sketch the graph of y = (x − 1)² + 4 and label the vertex and axis of symmetry.
Function Values — Continue the Pattern
Complete each table of function values.
Domain and Range Exploration
Determine the domain and range for each function.
State the domain and range of f(x) = x². Is any real number excluded?
State the domain and range of f(x) = √x. Why is the domain restricted?
State the domain and range of f(x) = 1/x. Which value of x is excluded and why?
Create a function whose domain is all real numbers but whose range is only positive numbers.
Types of Functions Encountered
Tally how many of each function type you have studied this week.
| Item | Tally | Total |
|---|---|---|
Linear | ||
Quadratic | ||
Exponential | ||
Hyperbolic | ||
Square root |
Relations vs Functions
Determine whether each relation is also a function and justify your answer.
Is {(1,2),(2,3),(3,4)} a function? Explain using the definition.
Is {(1,2),(1,3),(2,4)} a function? What rule does it violate?
Explain the vertical line test and why it works.
Give an example of a relation that is NOT a function. Draw its graph.
Function Notation — Evaluate Correctly
Circle the correct value of the function.
If f(x) = 2x + 3, then f(4) =
If g(x) = x² − 1, then g(−3) =
If h(x) = 3x − 5, then h(0) =
If f(x) = x² + x, then f(2) =
Composite and Inverse Functions
Explore how functions can be combined and reversed.
If f(x) = 2x and g(x) = x + 3, find f(g(x)) and g(f(x)).
Are f(g(x)) and g(f(x)) the same? What does this tell you about composition?
Find the inverse of f(x) = 3x − 6. Show all steps.
Check your inverse by computing f(f⁻¹(x)). What should you get?
Functions in Everyday Technology
Explore where mathematical functions appear in technology around you.
- 1Find a graph on your phone's screen time or health app. Identify the type of function it resembles.
- 2Look at a population graph for Australia. Is the growth linear, quadratic, or exponential? Justify.
- 3Open a spreadsheet and enter the formula =A1^2 for x = 1..10. Plot the result and describe the shape.
- 4Research how GPS uses mathematical functions to calculate your position. Write a short paragraph.
- 5Ask a family member what functions or graphs they use in their job. Report back to your class.
Piecewise Functions
Interpret and create piecewise-defined functions.
A taxi charges $3 flag fall plus $2/km. Write a function for the fare for x km.
A phone plan charges $0.10/min for the first 100 minutes, then $0.05/min after. Write a piecewise function for cost.
Evaluate your phone plan function at 80 minutes and at 150 minutes.
Draw a graph of the phone plan function for 0 ≤ x ≤ 200.
Transformations of Exponential Functions
Investigate how changing parameters affects exponential graphs.
Describe how y = 2^x + 3 differs from y = 2^x. What is the y-intercept of each?
Describe how y = 2^(x−1) differs from y = 2^x. In which direction is it shifted?
Sketch both y = 2^x and y = −2^x on the same axes. What is the relationship between them?
Write the equation of an exponential function that has been reflected in the x-axis and shifted up by 4 units. State its horizontal asymptote.
Function Types Graphed This Week
Tally each function type you graphed during this unit.
| Item | Tally | Total |
|---|---|---|
Linear | ||
Quadratic | ||
Exponential | ||
Hyperbolic | ||
Piecewise |
Sketching Quadratic Functions
Sketch parabolas by identifying key features.
For y = x² − 4x + 3, find the x-intercepts, y-intercept, axis of symmetry, and vertex. Show all working.
Sketch the parabola and label all key features found above.
Convert y = x² − 4x + 3 to vertex form y = (x−h)² + k. Show the completing-the-square process.