已知sin^4a+cos^4a=5/9,兀
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![已知sin^4a+cos^4a=5/9,兀](/uploads/image/z/4206268-28-8.jpg?t=%E5%B7%B2%E7%9F%A5sin%5E4a%2Bcos%5E4a%3D5%2F9%2C%E5%85%80)
已知sin^4a+cos^4a=5/9,兀
已知sin^4a+cos^4a=5/9,兀
已知sin^4a+cos^4a=5/9,兀
tanα+cotα=sinα/cosα+cosα+sinα=(sin^2α+cos^2α)/cosαsinα=1/sinαcosα
=2/sin2α
sin^2α=(1-cos2α)/2 cos^2α=(1+cos2α)/2
sin^4α+cos^4α=[(1-cos2α)/2]^2+[(1+cos2α)/2]^2
=1/2+1/2*cos^2(2α)=5/9
cos^2(2α)=1/9 sin^2(2α)=1-cos^2(2α)=8/9
π