Question

If `f(x)=x^2 + 2x +3`, then how do you find f(a-1)?

Answer 1

`a^2+2`

Explanation:

Substitute x = a-1 into function.

`rArrf(a-1)=(a-1)^2+2(a-1)+3`

expand brackets and collect like terms.

`rArr(a-1)^2+2(a-1)+3=a^2-2a+1+2a-2+3`

`=a^2+2`

Answer 2

It is enough to substitute `x` with `(a-1)`.

Explanation:

It is enough to write `(a-1)` every time that you read `x`.

`f(a-1)=(a-1)^2+2(a-1)+3`

then it is just a matter of doing a bit of algebra

`f(a-1)=(a-1)^2+2(a-1)+3`
`=a^2-2a+1+2a-2+3`
`=a^2+2`.