※ 引述《bboycookie (閉關BBOY餅乾)》之銘言：
: q:
: cosy dx-2(x-y)siny dy -cosy dy=0
: ans:
: 2 2
: xcos y - ycos y =c
cosy d(x-y)=2(x-y)siny dy
1
_______d(x-y)=2tany dy
(x-y)
ln(x-y)=-2ln(cosy)+c=ln((cosy)^-2)+ln(c*)
c*
x-y= ________
(cosy)^2
x(cosy)^2-y(cosy)^2=c*
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