(d) Let f(x, y) = 2x² + xy-y². Prove that the directional derivative of f(x, y) at point x = (3,-2) in the direction v=i- j is 2.

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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(b) Let r = xi + yj + zk, and let r= ||r. If f is a differentiable function of one
variable, show that
▼(f(r)r) = rf'(r) +3f(r)
(c) If and are smooth scalar fields, show that
▼x (6V) = Vox V
(d) Let f(x, y) = 2x² + xy-y². Prove that the directional derivative of f(x, y) at
point x = (3,-2) in the direction v = i- j is ¾.
Transcribed Image Text:(b) Let r = xi + yj + zk, and let r= ||r. If f is a differentiable function of one variable, show that ▼(f(r)r) = rf'(r) +3f(r) (c) If and are smooth scalar fields, show that ▼x (6V) = Vox V (d) Let f(x, y) = 2x² + xy-y². Prove that the directional derivative of f(x, y) at point x = (3,-2) in the direction v = i- j is ¾.
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