SOLUTION: Solve x^2+18x-4=0

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Question 131942: Solve
x^2+18x-4=0
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Complete the square. You do this by taking 1/2 of the coefficient of
the x term, square it, then add that to both sides of the
equation. First, add 4 to both sides
x%5E2+%2B+18x+-+4+=+0
x%5E2+%2B+18x+%2B+%2818%2F2%29%5E2+=+4+%2B+%2818%2F2%29%5E2
x%5E2+%2B+18x+%2B+81+=+4+%2B+81
%28x+%2B+9%29%5E2+=+85
Find square root of both sides
x+%2B+9+=+sqrt%2885%29
and
x+%2B+9+=+-sqrt%2885%29
sqrt%2885%29+=+9.2195
x+%2B+9+=+9.2195
x+=+.2195 answer
and
x+%2B+9+=+-9.2195
x+=+-18.2195 answer
check answers:
x%5E2+%2B+18x+-+4+=+0
%28.2195%29%5E2+%2B+18%2A.2195+-+4+=+0
.0482+%2B+3.951+-+4+=+0
3.9992+-4+=+0
close enough
%28-18.2195%29%5E2+-18%2A18.2195+-+4+=+0
331.95+-+327.951+-+4+=+0
3.999+-+4+=+0
close enough