Problem 4 (5 points). Consider the function f(x, y, z) = x + yz. Consider the curve parametrized by 1 r(t) = (cost (cost- sint)+ 1 (cost + sint)]+tk, 2 where 0 < t < 2. For each t, calculate the directional derivative of f at the point with positional vector (t) in the direction of the tangent vector to the curve at r(t)?