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Solve by completing the square; round to the nearest hundredth, if necessary. 3x^2+15x=108

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ryan133 | eNoter

Posted July 24, 2013 at 2:55 AM via web

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Solve by completing the square; round to the nearest hundredth, if necessary.

3x^2+15x=108

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aruv | High School Teacher | Valedictorian

Posted July 24, 2013 at 3:18 AM (Answer #1)

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`3x^2+15x=108`

factor out 3,

`x^2+5x=36`

`x^2+5x-36=0`

`x^2+2xx(5/2)x+(5/2)^2-(5/2)^2-36=0`

`(x+5/2)^2-(25/4+36)=0`

`(x+5/2)^2-((25+144)/4)=0`

`(x+5/2)^2=169/4`

`(x+5/2)^2=(+-13/2)^2`

Taking square root both side

`x+5/2=+-13/2`

`x=-5/2+-13/2`

`x=-5/2+13/2,-5/2-13/2`

`x=4,-9`

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