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Write the the function `f(x) = -5 x^2+30 x + 40` in the form `f(x)=a(x-p)^2+q` by completing the square:

1. We take out the coefficient of `x^2,` `a,` as a factor from the first two terms:

`f(x)=``(x^2+` `x)+ 40`

2. Then we add half of the coefficient of `x` squared, `(b/2)^2`, inside the bracket and subtract it outside `a` times, `a(b/2)^2`.

`f(x)=``(x^2+``x + ``)+ 40-`

3. Then we factorize the bracket and simplify outside the bracket.

`f(x)=``(x+``)^2+`

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Completing the square