Question

"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!

Answer 1

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