Algebra

Hello, 

$x^2-y^2=51+xy$

$x^2-y^2-xy=51$

$x^2-yx-y^2-51=0$

Solve with the quadratic formula:

$x_{1,\:2}=\frac{-\left(-y\right)\pm \sqrt{\left(-y\right)^2-4\cdot \:1\cdot \left(-y^2-51\right)}}{2\cdot \:1}$

$x_{1,\:2}=\frac{-\left(-y\right)\pm \sqrt{5y^2+204}}{2\cdot \:1}$.

I think you got $y$...

Let me know if you need help becoz this might get very messy.Good luck