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

Question

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

Answer 1

Hi again Kevin;

x²-4x

For the factor, this will be...

FIRST...(x)(x)=x².

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)=x²

OUTER...(x)(-2)=-2x

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

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

x²-2x-2x+4

x²-4x+4

 

The answer is 4.