I have the following problem and I've been trying to solve it

$\displaystyle \frac{6}{r^2-1}-\frac{1}{2}=\frac{1}{r+1}$

but when I try solving I just can't figure out how they get to 3 and -5. I'm supposed to solve it turning it into

$\displaystyle ax^2+bx+c=0$

I need to get rid of these denominators and therefore multiply the whole expression by its least common denominator

$\displaystyle 2(r^2-1)(r+1) $

but I stay stucked...!! Need guidance.