这也就说明了，可以用极坐标做二重积分。
The claim is we are able, to do double integrals in polar coordinates.
不是变量，这是在一个圆上。，R，is，not，a，variable。，You，are，on，the，circle。,这个是二重积分，如果你们这么做的话，在圆盘上，如果你们用极坐标的话,就需要用到R和θ
R This one is a double integral. So, if you are doing it, say, on a disk, you would have both R and theta if you're using polar coordinates.
请说，你想知道极坐标系下的积分边界，这是一个二重积分。
Yes? In case you want the bounds for this region in polar coordinates, indeed it would be double integral.
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