sin^2x+cos^2x=1y=1/sin^2x+2/cos^2x=(1/sin^2x+2/cos^2x)(sin^2x+cos^2x)=1+2+cos^2x/sin^2x+2sin^2x/cos^2x=3+cos^2x/sin^2x+2sin^2x/cos^2x>=3+2√[(cos^2x/sin^2x)(2sin^2x/cos^2x)]=3+2√2函数y=1/sin^x+2/cos^...