Question

If f(4x-15)=8x-27,findf°f(2)

Answer 1

f(4x-15)=8x-27.

Let y=4x-15, then x=(y+15)/4, 

So f(y)=8(y+15)/4-27=2y+30-27=2y+3.

And f(x)=2x+3.

f(2)=4+3=7.

f(7)=14+3=17, so f(f(2))=17=f∘f(2).

Answer 2

Let 4x-15=a

4x=a+15

X=(a+15)/4

f (4x-15)=8x-27

f [(4 (a+15)/4 )-15]=[8 (a+15)/4]-27

f (a+15-15)=[2 (a+15)]-27

f (a)= 2a+30-27

Or, f(x)=2x+3

f {f (x)}=2 {f (x)}+3

fof (x)=2 (2x+3) +3

fof (x)=4x+6+3

fof (x)=4x +9

fof (2)= 4*2 +9

fof (2)=8+9

fof (2)=17