[微積] 橢圓面績
求橢圓 x^2/a^2+y^2/b^2=1 之面積
let
x=acosu→dx=-asinu du
y=bsinu→dy= bcosu du
∫dA =∫∫dxdy
=∫∫-absinu*cosu dudu
今天跟老師討論了很久，但沒討論出什麼結果
覺得是少了變數r，極座標面積=rdrdθ
想請教上面的式子是從哪一步開始觀念出錯了？
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