Question

How do you solve by completing the square for `5-4x-x^2`?

Answer 1

I assume you meant to solve `5-4x-x^2 = 0`

This is equivalent to
`color(white)("XXXXX")` `x^2+4x = 5`
Completing the square
`color(white)("XXXXX")` `x^2+4x+4 = 5+4`
`color(white)("XXXXX")` `(x+2)^2 = 9`
Take the square root
`color(white)("XXXXX")` `x+2 = +-3`
Solve for x
`color(white)("XXXXX")` `x=-2+-3`

`x=-5` or `x=+1`