Im stuck on one of my questions in my book, i've got all the others right but this one has really stumped me. Im doing the same steps as the other questions so im pretty sure im missing something. I think im doin something wrong when im expanding each side of the equation and then simplifying.

Use the quadratic formula to solve the equation, rounding you answer to two decimal places.

$\displaystyle 2(x^2-1) = 15(x+3)$

$\displaystyle 2x^2-2 = 15x+45$

$\displaystyle 2x^2-15x-47=0$

$\displaystyle a=2, b=-15, c=-47$

$\displaystyle x= (--15) +- (sqrt)(-15^2 -4(2)(-47)))/4 $

$\displaystyle x= (15 +- (sqrt)151)/4$

$\displaystyle x= (15+(sqrt)151)/4 or (15-(sqrt)151)/4$

Does my attempt at writing the question make sense? Thanks :)

$\displaystyle x=6.82 or x=0.68$