What do you need to add to complete the square for x^2+8x?

1 Answer
Apr 1, 2018

16

Explanation:

Since the 8x is positive, the equation (x+y)^2 must have y as a positive number. Let's see this!

An easy way to complete the square if you have the constants for x^2 and x but not the non-variable number is to divide the x constant, and then square it. Just like this:

8x/2=4.
4^2=16.

The last number must be 16. Let's check it.

(x+4)^2=x^2+8x+color(red)16

The answer is 16.

Yay!