Let, $h$ is differentiable function. $\theta_1\in\mathbb{R}$, $\theta_2>0$ $$F(\theta_1,\theta_2) = \int_{\theta_1-\theta_2}^{\theta_1+\theta_2}\int_{\theta_1-\theta_2}^{y}n(n-1)\frac{(y-x)^{n-2}}{(2\theta_2)^n}h(x,y)dxdy$$
I need to find $\dfrac{\partial^2 F}{\partial \theta_1\partial \theta_2}$. I know Leibniz Rule for these type of cases. Is there any easy way to derive this? Thanks.