The answer is 16.
Since the 8x is positive, the equation must have y as a positive number.
Let's see this!
An easy way to complete the square if you have the constants for x2 and
But not the non-variable number is to divide the x constant, and then square it.
Example:
[tex]\frac{8x}{2} \\\\4^2=16\\[/tex]
The last number must be 16. Let's check it.
[tex](x+4)^2=x^2+8x+16[/tex]