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

3x^2+15x=108

### 1 Answer | Add Yours

`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`

### Join to answer this question

Join a community of thousands of dedicated teachers and students.

Join eNotes