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

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1 Answer

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.