SOLUTION: X^2 + 4x -8=0

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Question 757148: X^2 + 4x -8=0
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+x%5E2+%2B+4x+-+8+=+0+
You can complete the square
Take 1/2 of the coefficient of +x+,
square it, and add it to both sides
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First, add +8+ to both sides
+x%5E2+%2B+4x+=+8+
+x%5E2+%2B+4x+%2B+%284%2F2%29%5E2+=+8+%2B+%284%2F2%29%5E2+
+x%5E2+%2B+4x+%2B+4+=+8+%2B+4+
+x%5E2+%2B+4x+%2B+4+=+12+
+%28+x+%2B+2+%29%5E2++=+12+
Take the square root of both sides
+x+%2B+2+=+sqrt%2812%29+
+x+%2B+2+=+2%2Asqrt%283%29+
+x+=+-2+%2B+2%2Asqrt%283%29+
and, also,
+x+%2B+2+=+-sqrt%2812%29+
+x+=+-2+-2%2Asqrt%283%29+
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You can check the solutions by plugging them back
into the original equation
+x%5E2+%2B+4x+-+8+=+0+
+%28+-2+%2B+2%2Asqrt%283%29+%29%5E2+%2B+4%2A%28+-2+%2B+2%2Asqrt%283%29+%29+-+8+=+0+
+4+-+8%2Asqr%283%29+%2B+4%2A3+-+8+%2B+8%2Asqrt%283%29+-+8+=+0+
+4+%2B+12+-+8+-8+%2B+8%2Asqrt%283%29+-+8%2Asqrt%283%29+=+0+
+16+-+16+=+0+
+0+=+0+
OK -you can check other solution