Question

How do you write `f(x)=x^2+2x` in vertex form?

Answer 1

`(x+1)^2-1`

Explanation:

`f(x)=x^2+2x`
expanding this with `+1-1` gives:
`f(x)=x^2+2x+1-1` which is equivalent to `f(x)=x^2+2*1*x+1^2-1`
Now we can apply the reverse of the binomial formula and get:
`f(x)=(x+1)^2-1`