Question

21%

For all values of x
(2)
f(x) = (x + 2)2 and g(x) = 3(x - 1)
a) Find gf(x), giving your answer in the form a(x2 + bx + c)
where a, b and care integers.
(x² +
x +
b) Find g '(12)
(2)

Answer 1

f(x) = (x + 2)2 = 2x + 4

g(x) = 3(x - 1) = 3x - 3

gf(x) = (2x + 4)(3x - 3)

= 6x² - 6x + 12x - 12

= 6x² + 6x - 12

To write the final answer in the form

a(x² + bx + c) we factorize the expression

Thus

6x² + 6x - 12

= 6( x² + x - 2)

where a = 6, b = 1 and c = - 2

b.) to find g '(12) we first find g ′

To find g′ equate g(x) to y

Thus

g(x) = y

y = 3x - 3

x = 3y - 3

3y = x + 3

Divide both sides by 3

We get

y = x+3/3

That's g′ = x + 3 / 3

g′(12) = 12 + 3 / 3

= 15/3

= 5

Hope this helps