Find the directional derivative of z=x35y3\displaystyle {z}={x}^{{3}}-{5}{y}^{{3}} in the direction of θ=π4\displaystyle \theta=\frac{\pi}{{4}} at the point (0,0)\displaystyle {\left({0},{0}\right)}.

Duf(0,0)\displaystyle {D}_{{\vec{{u}}}}{f{{\left({0},{0}\right)}}} =