2.1
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![2.1](/uploads/image/z/15120909-45-9.jpg?t=2.1)
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2.1
2.1
2.1
x=asinb,y=acosb
1
1<=x^2+y^2<=2 推出 <=xy<= 推出1/2<=x^2+xy+y^2<=3
都算了~~
x^2+y^2>=2xy所以2xy<=2,xy<=1 x^2+y^2>=-2xy,2xy>=-(x^2+y^2)
而-(x^2+y^2)>=-2,xy>=-1
所以0<=x^2+xy+y^2<=3,题目好像打错了吧