If ax + by = a^2- b^2 and bx + ay =0, then the value of x + y is:

If $\displaystyle \mathrm{ax}+\mathrm{by}=\mathrm{a}^{2}-\mathrm{b}^{2}$ and $\displaystyle \mathrm{bx}+\mathrm{ay}=0$, then the value of $\displaystyle \mathrm{x}+\mathrm{y}$ is :