14. For each of the following functions, find the total differential (i.e. – df) at the indicated point: \text { a. } f(x)=4 x^{3} ; x_{0}=2 b.f(x)=(2x+10)^{1/2};x_0=3 \text { c.

} f(x, z)=-5 x^{2}+12 x z-2 z^{4} ; x_{0}=2, z_{0}=4 \text { d. } f(x, z)=10 x^{1 / 3} z^{2 / 3} ; x_{0}=8, z_{0}=8 \text { e. } f(x, z)=\left(5 x^{2}-7 z\right)\left(2 x+4 z^{3}\right) ; x_{0}=2, z_{0}=1