Marina solved the quadratic equation 9x^2-18x-720=8x^2-15x-640 by completing the square. In the process, she came up with the equivalent equation (x+r)^2 = s,where r and s are constants. What is s?
+605 $x^2-3x-80=0$. You know that $r=-\frac{3}{2}$ so to find $s$ subtract $\left(x-\frac{3}{2}\right)^2$ from the LHS.
