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what number would you add to the equation below to complete the square x^2 + 8x = 9

0 votes

this is a complete square problem.

asked Feb 21, 2014 in ALGEBRA 1 by linda Scholar

2 Answers

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Given equation x^2+8x = 9

Subtract 9 from each side.

x^2+8x-9 = 9-9

x^2+8x-9 = 0

To complete the squre add 25 to each side.

x^2+8x-9+25 = 0+25

x^2+8x+16 = 25

(x+4)^2 = 25

Apply squre root on each side.

x+4 = ±5

x+4 = 5 and x+4 = -5

Subtract 4 from each side.

x+4-4 = 5-4 and x+4-4 = -5-4

x = 1 and x = -9

Solution x = 1,-9.

answered Feb 21, 2014 by dozey Mentor
0 votes

The equation is x2 + 8x = 9.

To change the expression into a perfect square trinomial add (half the x coefficient)² to each side of the expression.

 Here x coefficient = 8. so, (half the x coefficient)² = (8/2)2= 16.

Add 16 to each side.

x2 + 8x + 16 = 9 + 16

(x + 4)2 = 25.

So, 16 is add to the equation x2 + 8x = 9 to complete the square.

answered Jun 4, 2014 by lilly Expert

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