gradient

f(x, y) = (sin(x) * cos(y)) + 1.5
theta = 0.5 (slider from -5 to 5)
A: (3, 1, 0)
M: (3, 1, f(3, 1))
B: A + (cos(theta), sin(theta), 0)
u = Vector(A, B)
p = Plane(A, B, M)
b = 1 (slider from -5 to 5)
c = Circle(A, b, xOyPlane)
eq1 = IntersectPath(p, f)