1.令x=sina,y=cosa
(1+xy)(1-xy)=1-(xy)^2=1-(1/(2sin2a))^2=1-(1-con4a)/8=7/8+con4a/8
所以最大值为1,最小值为3/4
2.最小值为4.
对于y=x+a/x,在(0,根号a】为减,在【根号a,正无穷)为增
1.令x=sina,y=cosa
(1+xy)(1-xy)=1-(xy)^2=1-(1/(2sin2a))^2=1-(1-con4a)/8=7/8+con4a/8
所以最大值为1,最小值为3/4
2.最小值为4.
对于y=x+a/x,在(0,根号a】为减,在【根号a,正无穷)为增