SOLUTION: use completing the square to discribe the graph of f(x)=36-12x-x^2 support your answer graphically

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Question 626967: use completing the square to discribe the graph of f(x)=36-12x-x^2
support your answer graphically
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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use completing the square to describe the graph of f(x)=36-12x-x^2
f(x) = 0
0 = 36 - 12x - x^2
x^2 + 12x + ___ = 36
Complete the square; (12/2)^2 = 36, add to both sides
x^2 + 12x + 36 = 36 + 36
x^2 + 12x + 36 = 72
(x + 6)^2 = 72
x + 6 = +/-sqrt%2872%29
extract the square root of 36
x + 6 = +/-6sqrt%282%29
Two solutions
x = -6+%2B+6sqrt%282%29
and
x = -6+-+6sqrt%282%29
;
support your answer graphically
+graph%28+300%2C+200%2C+-20%2C+20%2C+-80%2C+50%2C+x%5E2%2B12x-36%29+
:
-6+%2B+6sqrt%282%29 ~ +2.5
-6+-+6sqrt%282%29 ~ -14.5