Question

Find the directional derivative of f(x,y)=x^2y^3 + 2x^4y at the point (2, 5) in the direction θ=5π/6.

I found $$\nabla f(2,5) = <820, 332>$$

How do i find the directional derivative?

Answer 1

I reckon that the directional derivative
df/ds = |grad f| cosθ

Answer 2

@alekos ah, got it, ty :)!

Answer 3

its 820 * cos(5pi/6) + 332 * sin(5pi/6)

Answer 4

i was making it more complicated in my head than it really was

Answer 5

yes, that would be it as well
the dot product of gradf and (cosθ,sinθ) where θ = 5π/6