SOLUTION: Could you help me solve the equation of {{{ x^2+12x=15 }}}

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Question 559338: Could you help me solve the equation of ++x%5E2%2B12x=15++
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
++x%5E2%2B12x+=+15++
You can solve by completing the square.
Take 1/2 of the coefficient of x,
square it, and add it to both sides
+x%5E2+%2B+12x+%2B+%2812%2F2%29%5E2+=+15+%2B+%2812%2F2%29%5E2+
+x%5E2+%2B+12x+%2B+36+=+15+%2B+36+
+%28+x+%2B+6+%29%5E2+=+51+
Take the square root of both sides
+x+%2B+6+=+sqrt%28+51+%29+
+x+=+sqrt%2851%29+-+6+
and also, taking the negative square root,
+x+=+-sqrt%2851%29+-+6+
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I will attempt to check the 1st solution
+%28+sqrt%2851%29+-+6%29%5E2%2B12%2A%28+sqrt%2851%29+-+6%29+=+15+
+51+-+12%2Asqrt%2851%29+%2B+36+%2B+12%2Asqrt%2851%29+-+72+=+15+
+51+%2B+36+-+72+=+15+
+15+=+15+
OK
You can check the other solution, +x+=+-sqrt%2851%29+-+6+