Find the grad (vector calculus)

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SUMMARY

The discussion focuses on demonstrating the gradient of the vector function grad(r.\hat{k}/r^3), where r is defined as r = xi + yj + zk and \hat{k} represents the unit vector in the z-direction. The solution confirms that the expression grad(r.\hat{k}/r^3) simplifies to [r^2\hat{k}-3(r.\hat{k})r]/r^5. The participants clarify that the formula applies to any constant vector 'k' and utilize the quotient rule for gradients, grad(f/g) = grad(f)/g - f*grad(g)/g^2, to derive the result.

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  • Understanding of vector calculus concepts, specifically gradients.
  • Familiarity with scalar functions and their properties.
  • Knowledge of the quotient rule for differentiation.
  • Basic understanding of unit vectors and their applications.
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Homework Statement



show that
grad(r.[tex]\hat{k}[/tex]/r^3) = [r^2[tex]\hat{k}[/tex]-3(r.[tex]\hat{k}[/tex])r]/r^5

Homework Equations





The Attempt at a Solution



I know that r=xi+yj+zk
and i know how to calculate the grad from the formula but, what is r.[tex]\hat{k}[/tex] ?
thank you
 
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r.k=z. So you can just show it directly by showing both sides are equal. But actually that formula holds for any constant vector 'k'. If f is a scalar function (like r.k) and g is a scalar function (like r^3), grad(f/g)=grad(f)/g-f*grad(g)/g^2. That's what the two different terms on the right side are.
 

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