Three term quadratic?

Express x2−2x−15 in the form (x+a)2+b.

1 Answer
Jim G.
Sep 12, 2017

(x−1)2−16

Explanation:

using the method of completing the square

∙ ensure the coefficient of the x2 term is 1

∙ add/subtract (12coefficient of x-term)2 to x2−2x

⇒x2−2x−15

=x2+2(−1)x+1−1−15

=(x−1)2−16←a=−1,b=−16

As a check for you

(x−1)2−16

=x2−2x+1−16

=x2−2x−15

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