Find the Directional derivative of the function u

[asi123]

Homework Statement

Hey.
I need to find the Directional derivative of the function u, in the direction l, in the point m (all in the pic).
I'm not sure I did it right, can you please give me the ok?

Homework Equations

The Attempt at a Solution

 

[HallsofIvy]

Up to D_Lu= (1/3)(2x- z)+ (2/3)cos y+ (2/3)x, everything looks good. Then you evaluate that at $(1,\pi/2, -3)$ and get 7/10? That's not what I get.

 

[asi123]

Up to D_Lu= (1/3)(2x- z)+ (2/3)cos y+ (2/3)x, everything looks good. Then you evaluate that at $(1,\pi/2, -3)$ and get 7/10? That's not what I get.

Oops, got 7/3?

 

[HallsofIvy]

Yes, that is correct. I wondered where that "10" came from!

 

[asi123]

Yes, that is correct. I wondered where that "10" came from!

Broken calculator...

No, just kidding, it was early in the morning.