x^2 + 8x -78=-5 Solve by completing the square.
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jgeertz
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`x^2+8x-78=-5`
Add `78` to both sides.
`x^2+8x= 73`
In order to create a trinomial square on the left side of the equation, add a value to both sides that is equal to the square of half the coefficient of `x` . In this case, add `4^2` to both sides.
`x^2+8x+16=73+16`
`x^2+8x+16=89`
Now factor the perfect trinomial square.
`(x+4)^2 =89`
Take the square root of each side of the equation.
`(x+4)^(2/2) = +-sqrt89`
`x+4 =+-sqrt89`
`x= +sqrt89 -4`
`x=-sqrt89 -4`
The complete solution is:
`x=sqrt89 - 4, -sqrt89-4`
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