Completing the square to solve 3x^2 + 7x = -9

[yoda]

Solve by completing the square:

. . .3x^2 + 7x = -9

My teacher gave me the answer but I can't figure out how she got it. When I went in to talk to her, I just got more confused. Can someone please help me figure out how to solve by completing the square?

Thank you!

 

[galactus]

Here's an equation to use when completing the square. Your teacher probably wants you to go through the steps, though. The leading coefficient of 3 must be accounted for.

You have \(\displaystyle \L\\\underbrace{3}_{\text{a}}x^{2}+\underbrace{7}_{\text{b}}x+\underbrace{9}_{\text{c}}\)

\(\displaystyle \L\\a(x+\frac{b}{2a})^{2}+\underbrace{c-\frac{b^{2}}{4a}}_{\text{constant}}\)

 

[yoda]

ok i got it now... surprisingly... thanks!