Question

Complete the square.

x^2 + _____ + 36

Help me? I don't understand.

Answer 1

well, 6^2 = 36
So, you want (x+6)^2 = x^2 + 12x + 36

recall that (x+a)^2 = x^2 + 2ax + a^2

Answer 2

well, 36 = 6^2 so try

x^2 + b x + 36 = (x+6)^2

x^2 + b x + 36 = x^2 + 12 x + 36
so

x^2 + 12 x + 36
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more officially
(b/2)^2 = 36
b/2 = 6
b = 12