SOLUTION: Solve the equation by completing the square. Round to the nearest hundredth if necessary. x2 + 2x = 17

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Question 1088722: Solve the equation by completing the square. Round to the nearest hundredth if necessary. x2 + 2x = 17
Found 2 solutions by natolino_2017, josmiceli:
Answer by natolino_2017(77) About Me  (Show Source):
You can put this solution on YOUR website!
First remember the formula: (x+a)^2 = x^2 + 2ax + a^2.
so (x+1)^2 = x^2 + 2x + 1.
using this on x^2 + 2x = 17

(x+1)^2 - 1 = 17
(x+1)^2 = 18
abs(x+1) = sqrt(18) = 3sqrt(2)
so x = -1 +3sqrt(2) or x = -1 -3sqrt(2)
aproaching to the nearest hundreth:
x={3.24;-5.24}
@natolino_

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+x%5E2+%2B+2x+=+17+
Take 1/2 of the x term, square it,
and add it to both sides
+x%5E2+%2B+2x+%2B+%282%2F2%29%5E2+=+17+%2B+%282%2F2%29%5E2+
+x%5E2+%2B+2x+%2B+1+=+18+
+%28+x+%2B+1+%29%5E2+=+%28+sqrt%2818%29+%29%5E2+
+x+%2B+1+=+sqrt%2818%29+
--------------------------------
+x+=+3%2Asqrt%282%29+-+1+
and, taking the negative square root:
+x+=+-3%2Asqrt%282%29++-+1+
--------------------------
check:
+x%5E2+%2B+2x+=+17+
+%28+3%2Asqrt%282%29+-+1+%29%5E2+%2B+2%2A%28+3%2Asqrt%282%29+-+1+%29+=+17+
+18+-+6%2Asqrt%282%29+%2B+1+%2B+6%2Asqrt%282%29+-+2+=+17+
+18+-+2+%2B+1+=+17+
+17+=+17+
OK
You can check the other solution