$x^p y^q=(x+y)^{p+q}$ what is the value of $y_2$

$x^p y^q=(x+y)^{p+q}$ what is the value of $y_2$

If $x^p y^q=(x+y)^{p+q}$ then how to compute ${d^2 y}\over{dx^2}$
The result is 0