Question

F is the function such that f(x)=2x-5 g is the function such that g(x)=x^2-10 can you solve gf(x)=-1?

I have done the function of f(x) but I'm confused whether my answer to f(x) substitutes for x or y.

Answer 1

`gf(x)=(2x-5)^2-10`

`gf(x)=4x^2-20x+25-10`

`gf(x)=4x^2-20x+15`

If `gf(x)=-1` then `4x^2-20x+15=-1`

`4x^2-20x+16=0`

divide by 4

`x^2-5x+4=0`

`(x-4)(x-1)=0`

`x=4 or x=1`

Putting both these values into `f(x)` and then the answer into `g(x)` gives -1 as the solution