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 $$ abla f(2,5) = $$ How do i find the directional derivative?

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 $$
abla f(2,5) = <820, 332>$$

How do i find the directional derivative?

alekos · Answer

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

anonymous · Answer

@alekos ah, got it, ty :)!

anonymous · Answer

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

anonymous · Answer

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

alekos · Answer

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