Complete the square

Complete the square. Fill in the number that makes the polynomial a perfect-square quadratic.

x² + 8x +

Add to complete the square.

x² + 8x +

=	x2 + 8x +		Plug in b=8
=	x2 + 8x +		Divide
=	x2 + 8x + 42		Square
=	x2 + 8x + 16

This quadratic can be written as a square, (x + 4)², so it is a perfect-square quadratic.

The number needed to complete the square was 16.