解ï¼ä»¤x=sint,y=cost
令Y=(x+y+2)/(x-y+2)=(sinx+cosx+2)/(sinx-cosx+2)
æ´çæ(1-Y)sint+(1+Y)cost=2(y-1)
(1-Y)sint+(1+Y)cost=â[(1-Y)²+(1+Y)²]sin(t+Ï)=2(Y-1)
|sin(t+Ï)|â¤1å |â[(1-Y)²+(1+Y)²]|â¥2|(Y-1)|
两边平æ¹å¾Y²-4Y+1â¤0
解å¾ï¼2-â3â¤Yâ¤2+â3å¾ææ±å¼çæ大å¼åæå°å¼åå«2+â3,2-â3
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