$(6\%)A$ scalar function $f=f(x,y,z)=f(r,,),$ and $x=x(r,,)=rsincos,y=y(r,,)=$

$rsinsin,z=z(r,,)=rcos,$ express $\frac{\text{d}\text{e}\text{l}\text{f}}{\text{d}\text{e}\text{l}}in$ terms $of\frac{\text{d}\text{e}\text{l}\text{f}}{\text{d}\text{e}\text{l}\text{x}},\frac{\text{d}\text{e}\text{l}\text{f}}{\text{d}\text{e}\text{l}\text{y}},\frac{\text{d}\text{e}\text{l}\text{f}}{\text{d}\text{e}\text{l}\text{z}}$ and $r,,.$