Question

Jika f(x) = (1 + 4x).2.(2 – x), maka 6.f '(1) + f '(–1) = . . . .

Answer 1

f(x)= (2+8x)(2-x)=-8x^2+14x+4
maka f'(x)= -16x+14
jadi 6(-16(1)+14)-(-16(-1)+14)=6(-2)-(30)=-12-30=-42

Answer 2

f(x) = (2+8x)(2-x) atau (8x-2)(x+2) = -8x² + 14x - 4 
f'(x) = -8.2x + 14
f'(x) = -16x + 14

6f'(1) = -16 + 14 = -2 x 6 = -12
f'(-1) = 16 + 14 = 30

6f'(1) + f(-1) 
= -12 + 30 
= 18