\text { Find the first partial derivatives of } f(x, y)=x^{3} y \sqrt{3 x y-7} \text { Find the } \frac{\partial^{3} f}{\partial x \partial z \partial y} \text { where

} f(x, y, z)=5 y^{3} x \sin \left(y z^{2}-5 y\right) \text { ] Find a point } P(a, b) \text { such that } \frac{\partial^{2} f}{\partial x \partial y}(a, b)=0 \text { where } f(x, y)=3 y^{2} x^{2}(4 x+3 y)