Thomas Calculus Chapter 14 Exercise 14.5 Q15:
Find the derivative of the function at Po in the direction of u.
f(x, y, z) = xy + yz + zx , Po = (1, -1, 2), u = 3i + 6j - 2k
The answer given in the solution of this website stated 21 using the concept of limits.
However, I tried another method using partial derivatives and get the answer of 3 instead. Could anyone help check which method and answer is correct. Thanks!