HSC/VCE-style Functions and Graphs Practice with Worked Solutions — Answers
Answer sheet with worked solutions for the Year 12 functions worked examples.
Year 12 · Mathematics · Functions
HSC/VCE-style Functions and Graphs Practice with Worked Solutions — Answers
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Section A: Notation, domain, range and transformations
1.f(x) = x2 − 2x. Find f(3) and f(−1).[2 marks]
Answer: f(3) = 3 and f(−1) = 3
- f(3) = 32 − 2(3) = 9 − 6 = 3
- f(−1) = (−1)2 − 2(−1) = 1 + 2 = 3
- (Both points lie at the same height because the parabola is symmetric about x = 1.)
2.State the natural domain and the range of f(x) = √(2x − 6).[2 marks]
Answer: Domain x ≥ 3; range y ≥ 0
- The expression under the root must be non-negative: 2x − 6 ≥ 0.
- 2x ≥ 6, so x ≥ 3. Domain: x ≥ 3.
- The square root function gives outputs from 0 upwards, with f(3) = 0. Range: y ≥ 0.
3.g(x) = . State the natural domain of g, and find g(0).[3 marks]
Answer: Domain: all real x except x = 3 and x = −3; g(0) = −
- The denominator cannot be zero: x2 − 9 ≠ 0.
- (x − 3)(x + 3) ≠ 0, so x ≠ 3 and x ≠ −3.
- Domain: all real x, x ≠ ±3.
- g(0) = = = −
4.The point (1, 4) lies on the graph of y = f(x). Find the coordinates of its image on (a) y = 2f(x − 3) + 1 and (b) y = f(−x).[3 marks]
Answer: (a) (4, 9) (b) (−1, 4)
- (a) x − 3 shifts the graph 3 units right: x becomes 1 + 3 = 4.
- The factor 2 doubles the y-value: 4 × 2 = 8. The + 1 then shifts it up: 8 + 1 = 9.
- Image: (4, 9).
- (b) f(−x) reflects the graph in the y-axis, so x changes sign and y is unchanged.
- Image: (−1, 4).
Section B: Composite, inverse, odd and even functions
5.f(x) = 2x + 1 and g(x) = x2. Find (a) f(g(x)), (b) g(f(x)) and (c) f(g(2)).[3 marks]
Answer: (a) 2x2 + 1 (b) 4x2 + 4x + 1 (c) 9
- (a) f(g(x)) = f(x2) = 2x2 + 1
- (b) g(f(x)) = g(2x + 1) = (2x + 1)2 = 4x2 + 4x + 1
- (c) g(2) = 4, so f(g(2)) = f(4) = 2(4) + 1 = 9. (Check with part (a): 2(2)2 + 1 = 9.)
6.f(x) = , x ≠ 2. Find the inverse function f−1(x) and state its domain.[3 marks]
Answer: f−1(x) = + 2, domain x ≠ 0
- Write y = and swap x and y: x = .
- Make y the subject: x(y − 2) = 3, so y − 2 = .
- y = + 2, so f−1(x) = + 2.
- The domain of f−1 is the range of f. f never equals 0 (its horizontal asymptote is y = 0), so the domain of f−1 is x ≠ 0 — which also matches the in the rule.
7.Determine whether each function is even, odd or neither: (a) f(x) = x3 − 4x, (b) g(x) = x4 + 2x2, (c) h(x) = x2 + x.[3 marks]
Answer: (a) odd (b) even (c) neither
- A function is even if f(−x) = f(x) and odd if f(−x) = −f(x).
- (a) f(−x) = (−x)3 − 4(−x) = −x3 + 4x = −(x3 − 4x) = −f(x), so f is odd (symmetric about the origin).
- (b) g(−x) = (−x)4 + 2(−x)2 = x4 + 2x2 = g(x), so g is even (symmetric about the y-axis).
- (c) h(−x) = x2 − x. This is not equal to h(x) = x2 + x, and not equal to −h(x) = −x2 − x, so h is neither.
Section C: Key features of graphs
8.For the parabola y = (x − 2)2 − 9, find the vertex, the y-intercept, the x-intercepts and the range.[4 marks]
Answer: Vertex (2, −9); y-intercept −5; x-intercepts x = −1 and x = 5; range y ≥ −9
- Vertex form y = (x − h)2 + k gives the vertex (2, −9). It is a minimum because the coefficient of x2 is positive.
- y-intercept (x = 0): y = (−2)2 − 9 = 4 − 9 = −5.
- x-intercepts (y = 0): (x − 2)2 = 9, so x − 2 = ±3, giving x = 5 or x = −1.
- Range: the minimum value is −9, so y ≥ −9.
9.For the hyperbola y = − 3, state the equations of the asymptotes and find the coordinates of the intercepts with the axes.[4 marks]
Answer: Asymptotes x = −1 and y = −3; y-intercept (0, −1); x-intercept (−, 0)
- The base graph y = is shifted 1 unit left (x + 1) and 3 units down (− 3).
- Vertical asymptote: x + 1 = 0, so x = −1. Horizontal asymptote: y = −3.
- y-intercept (x = 0): y = − 3 = −1, so (0, −1).
- x-intercept (y = 0): = 3, so 3(x + 1) = 2, x + 1 = , x = −. Point (−, 0).
10.For the curve y = 2x − 8, find the y-intercept, the x-intercept, the equation of the horizontal asymptote and the range.[4 marks]
Answer: y-intercept −7; x-intercept x = 3; asymptote y = −8; range y > −8
- y-intercept (x = 0): y = 20 − 8 = 1 − 8 = −7.
- x-intercept (y = 0): 2x = 8 = 23, so x = 3.
- As x → −∞, 2x → 0, so y → −8 from above. Horizontal asymptote: y = −8.
- 2x > 0 for all x, so y = 2x − 8 > −8. Range: y > −8.
Marking tips
- Give credit for correct method even when the final answer slips — the working shows where the thinking went right.
- For open-ended tasks, use the success criteria as a checklist rather than looking for one "right" answer.
- Celebrate what went well first, then pick one thing to work on next.