Thursday, 28 February 2019

calculus - Integral of a gradient over a plane area

Let $A$ be a plane area bounded by a curve $\partial A$. Then, is



$$ \iint_A \nabla f\, \textrm{d}x \textrm{d}y = \oint_{\partial A} f\ \hat{\mathbf{n}}\ dl $$



where $f=f(x,y)$ and $\mathbf{\hat n}$ is the outward unit normal?

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