- #1

rbwang1225

- 118

- 0

##\bf a = ∫_S d \bf a##, where S is the surface and ##\bf a ##is the vector area of it.

Please proof that ##\bf a = \frac{1}2\oint \! \bf r \times d\bf l##, where integration is around the boundary line.

Any help would be very appreciated!