Question

HELP ASAP! Find the zeros of y = x^2 - 8x - 3 by completing the square.

Answer 1

Notice (x+4)2 = x2 + 8x +16 which differs from the question by a constantSo we can write: 

x2 + 8x + 3 = (x+4)2 - 13     

(x+4)2 -13 = 0

(x+4)2 = 13     (by adding 13)

x+4 = +-sqrt(13)    (square root remembering to include the +-)

x = -4 +-sqrt(13)      (subtracting 4)

So we have answers of:

x = - 4 + sqrt(13)

x = - 4 - sqrt(13)

which can both be checked by substitution into the or