Question

How do you solve by completing the square `x^2+8x-9=0`?

Answer 1

The quadratic that is a square and starts with the terms `x^2` and `8x`
is `x^2+8x+16`

Re-write the given equation with the square quadratic at the beginning
`x^2+8x+16-25 = 0`

`(x+4)^2 = 25`

`x+4 = +-sqrt(25)`

`x=-4+-5`

`x=-9` or `x=1`