SOLUTION: Solve by completing the square: x^2 - 16x + 63 = 0 I have four answers: a) -7, 9 b) 7,9 C) 7, -9 D) -7, -9 When I plug in these answers, I do not come up with zero, am I

Algebra ->  Equations -> SOLUTION: Solve by completing the square: x^2 - 16x + 63 = 0 I have four answers: a) -7, 9 b) 7,9 C) 7, -9 D) -7, -9 When I plug in these answers, I do not come up with zero, am I      Log On


   

Question 69891: Solve by completing the square:
x^2 - 16x + 63 = 0
I have four answers:
a) -7, 9
b) 7,9
C) 7, -9
D) -7, -9
When I plug in these answers, I do not come up with zero, am I doing something wrong? Thank you for your help!
Answer by ptaylor(2198) About Me  (Show Source):
You can put this solution on YOUR website!
Solve by completing the square:
x%5E2+-+16x+%2B+63+=+0
A=1
B=-16
C=+63
First, subtract 63 from both sides:
x%5E2-16x=-63
Now we will force the left side of the equation to become a perfect square. We will do this by taking half of the B coefficient, squaring it and then adding the result to both sides:
Half of 16 is 8 and 8 squared is 64---add this to both sides:
x%5E2-16x%2B64=-63%2B64 Note that the left side is a perfect square:
%28x-8%29%5E2=1
take square root of both sides:
%28x-8%29=0%2B-sqrt%281%29
x=8%2B-sqrt%281%29
x=8-1
x=7----------------------------ans
and
x=8%2B1
x=9--------------------ans
CK
7%5E2-16%2A7%2B63=0
49-112%2B63=0
-63%2B63=0
0=0
Also
9%5E2-16%2A9%2B63=0
81-144%2B63=0
-63%2B63=0
0=0

Hope this helps---ptaylor