令x=cosa,y=sina
x^+xy-y^
=cosa^2+sinacosa-sina^2
=cos2a+1/2sin2a
|x^+xy-y^|≤√5/4<√2
我认为应该是x^+2xy-y^
这样的话,x^+xy-y^=cos2a+sin2a
|x^+xy-y^|≤√2
令x=cosa,y=sina
x^+xy-y^
=cosa^2+sinacosa-sina^2
=cos2a+1/2sin2a
|x^+xy-y^|≤√5/4<√2
我认为应该是x^+2xy-y^
这样的话,x^+xy-y^=cos2a+sin2a
|x^+xy-y^|≤√2