Directional derivative
posted by Anonymous .
"Find the directional derivative fu(1,2) for the function f with u = (3i4j)/5 for f(x,y)= x^(2)  y^(2)."
Thank you!

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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