How do you solve x2−8x=9 by completing the square?

2 Answers
Nghi N.
Jul 7, 2015

Solve y = x^2 - 8x - 9 = 0

Explanation:

In this case, you don't need to solve by completing the squares.
Use the shortcut.
When (a - b + c = 0) --> 2 real roots: (-1) and (-c/a = 9).

MeneerNask
Jul 7, 2015

You take half the x-coefficient (−8→−4) and square it (16)

Explanation:

This means you have to add 16 to both sides of the equation:
x2−8x+16=9+16→
(x−4)2=25→
So: x−4=√25=5→x=9
Or: x−4=−√25=−5→x=−1

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