2 (a) If

u= x¹y+y²z³,

where x = rset, y = rs²e-¹ and z = r² sin t, find the value of

=

du

Əs

when r = 2, s = 1, t = 0.

[5 marks]

(b) Suppose that over a certain region of space the potential is given

by

(x, y, z) = x sin(yz).

Find the directional derivative of the potential at the point P (1,3,0)

in the direction of the vector v=i+2j - k.

[5 marks]