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Homework Statement
Q1. Evaluate grad(f) for the function f([tex]\underline{r}[/tex])=([tex]\underline{a}[/tex] dot [tex]\underline{r}[/tex]) ([tex]\underline{b}[/tex] dot [tex]\underline{r}[/tex])
Q2. If [tex]\underline{c}[/tex] is a constant vector, show that grad |[tex]\underline{c}[/tex] cross [tex]\underline{r}[/tex]| ^n = n |[tex]\underline{c}[/tex] cross [tex]\underline{r}[/tex]| ^(n-2) *[tex]\underline{c}[/tex] cross ([tex]\underline{r}[/tex] cross [tex]\underline{c}[/tex] )
Homework Equations
dot product and cross product identities
formula for grad f
The Attempt at a Solution
Q1, I tried to expand it use product rule but simplified it back to where I started, I don't see how I can simplify the result.
Q2, used chain rule got n |[tex]\underline{c}[/tex] cross [tex]\underline{r}[/tex]| ^(n-2) *([tex]\underline{c}[/tex] cross [tex]\underline{r}[/tex] )
btw I have proven that grad r^n = n * r^ (n-2) * [tex]\underline{r}[/tex], not sure if this is correct.
This is my first post, hopefully it is understandable..
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