Absolute and Relatiave Uncertainty (partial derivatives)

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Homework Statement



Calculate the following, expressing all results with uncertainties both in absolute and relative (percentage) form:

a) A + B

b) A x B

c) Asin(theta)

d) A^2 / Bcos(theta)


The relevant formula for the absolute uncertainty is below, but i have no idea how to use it! The teacher just sort of gave us the assignment without much explanation.. I know that it uses something called partial derivatives, could someone explain how to find that?
 

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Assuming you know how to take derivatives, a partial derivative is just holding all the other variables as constant.

So if we had z=xy and we wanted to get ∂z/∂x, we would hold 'y' constant and differentiate like normal to get ∂z/∂x = y.

For this exercise, you should at least know how to take derivatives.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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