Home / iGCSE Mathematics (0580) :E2.13 Understand the idea of a derived function.iGCSE Style Questions Paper 2

iGCSE Mathematics (0580) :E2.13 Understand the idea of a derived function.iGCSE Style Questions Paper 2

Question

(a) Given:

f(x) = 4x + 3

g(x) = 5x − 4

fg(x) = 20x + p

Find the value of p.

(b) Given:

\( h(x) = \frac{5x – 1}{3} \)

Find \( h^{-1}(x) \).

▶️ Answer/Explanation
Answers:

(a) p = −13 → Substitute g(x) into f(x): fg(x) = f(5x−4) = 4(5x−4) + 3 = 20x − 16 + 3 = 20x − 13.

(b) \( h^{-1}(x) = \frac{3x + 1}{5} \) → Swap x and y, then solve for y: \( x = \frac{5y – 1}{3} \) → 3x = 5y − 1 → y = (3x + 1)/5.

Question

(a) \(f(x)=3x^{2}+a\) where a is an integer.
f(-2)=19
Find the value of a.

(b) g(x)=2x+7       h(x)=3x-8
(i) Find gh(x) in its simplest form.
(ii) Find \(g^{-1}(x)\).

▶️ Answer/Explanation
Answer:
(a) a = 7
(b)(i) 6x – 9 or 3(2x – 3)
(ii) \(\frac{x-7}{2}\)
Explanation:
(a) Substitute x=-2: 3(-2)² + a = 19 → 12 + a = 19 → a=7
(b)(i) gh(x) = g(h(x)) = 2(3x-8)+7 = 6x-9
(ii) Swap x and y: x=2y+7 → y=(x-7)/2
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