# Thread: [SOLVED] Completing the square

1. ## [SOLVED] Completing the square

How do you complete the square of this problem?

$5-4x-x^2$

2. Originally Posted by Mike9182
How do you complete the square of this problem?

$5-4x-x^2$
Divide the expression by -1 to get a positive coefficient of $x^2$

$-(x^2+4x-5)$

When completing the square divide $b$ by 2:

$(x+2)^2$. However this gives us $x^2+4x+4$ so we must take 4 to get the expression to work (and don't forget c)

$-[(x+2)^2 - 4 -5] = -[(x+2)^2-9] = 9-(x+2)^2$

3. Thanks, what about this one? $4x-x^2$?