Posted by **Anonymous** on Sunday, February 27, 2011 at 11:25pm.

"Find the directional derivative fu(1,2) for the function f with u = (3i-4j)/5 for f(x,y)= x^(2) - y^(2)."

Thank you!

- Directional derivative -
**agrin04**, Monday, February 28, 2011 at 2:14am
df(x,y)/dx = 2x

df(1,2)/dx = 2

df(x,y)/dy = -2y

df(1,2)/dy = -4

Directional derivative =

= <2,-4> • <(3/5),-(4/5)>

= (6/5) + (16/5)

= 22/5

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