How do you complete the square to solve x^2 + 4x = 12?

1 Answer
Don't Memorise
May 31, 2015

x^2 + 4x = 12

To write the Left Hand Side as a Perfect Square, we add 4 to both sides:

x^2 + 4x +4= 12+4
x^2 + 2*2*x + 2^2 = 16
Using the Identity color(blue)((a+b)^2 = a^2 + 2ab + b^2, we get
(x+2)^2 = 16
x + 2 = +sqrt16 or x +2 = -sqrt16
x = + 4 -2 or -4 -2
color(blue)(x = 2 or x=-6

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