Question

Diketahui f(2x+3) = 5x-8.
nilai f(-1)?

Answer 1

2x+3 = p
x = 1/2(p-3)

F(p) = 5/2(p-3) - 8
F(p) = 2,5p - 7,5 - 8
F(p) = 2,5p + 0,5
F(x) = 2,5x + 0,5
F(-1) = 2,5(-1) + 0,5
= -2,5 + 0,5 = -2

Answer 2

Cari invers nya dulu:
Y=2x+3, 
(y-3)/2=x, 
y=f(x)= (x-3)/2,

maka:
f(x)=5((x-3)/2) -8 , 

sehingga:
f(-1)= 5((-1-3)/2) -8 
=5(-2)-8,
=-10-8,
= -18