The number that should be added to x^2-4x to complete the square is ?

Hi again Kevin;

x

^{2}-4xFor the factor, this will be...

FIRST...(x)(x)=x

^{2}.OUTER and INNER must add-up to be -4x.

LAST must be (3)(1) or (1)(3) or (2)(2). It must be (2)(2) because we are completing a square.

(x-2)(x-2)

(x-2)

^{2}Let's FOIL...

FIRST...(x)(x)=x

^{2}OUTER...(x)(-2)=-2x

INNER...(-2)(x)=-2x

LAST...(-2)(-2)=4

x

^{2}-2x-2x+4x

^{2}-4x+4The answer is 4.