Find the grad (vector calculus)

In summary, the problem is asking to show that grad(r.\hat{k}/r^3) is equal to [r^2\hat{k}-3(r.\hat{k})r]/r^5. The formula for calculating grad is known, but there is confusion about r.\hat{k}. It is clarified that r.\hat{k}=z, and the solution can be shown directly by equating the two sides. Additionally, the general formula for calculating grad of a scalar function divided by another scalar function is provided as f/g=grad(f)/g-f*grad(g)/g^2.
  • #1
sara_87
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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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  • #2
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.
 

1. What is the definition of gradient in vector calculus?

The gradient is a vector operator that operates on a scalar field, resulting in a vector that points in the direction of the steepest increase of the scalar field at a given point.

2. How do you find the gradient of a function in vector calculus?

To find the gradient of a function, you take the partial derivatives of the function with respect to each variable and combine them into a vector. This vector represents the direction and magnitude of the steepest increase of the function at any given point.

3. What is the relationship between the gradient and the derivative in vector calculus?

The gradient is closely related to the derivative in vector calculus. The gradient is essentially a generalization of the derivative in higher dimensions, as it takes into account all partial derivatives of a function instead of just one. In one-dimensional calculus, the gradient is equivalent to the derivative.

4. How is the gradient used in vector calculus?

The gradient is used in many applications in vector calculus, including optimization problems, vector field analysis, and solving differential equations. It helps us understand the direction and rate of change of a function and can be used to find the minimum or maximum values of a function.

5. Can the gradient be negative in vector calculus?

Yes, the gradient can be negative in vector calculus. A negative gradient indicates that the function is decreasing in that direction, while a positive gradient indicates an increase. The magnitude of the gradient represents the rate of change in that direction.

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