已知sin²2a+sin2acosa-cos2a=1,a属于(0,π/2),求sina,t

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sin²2a+sin2acosa-cos2a=1
(2sinacosa)^2+2sina(cosa)^2-2(cosa)^2+1=1
2(cosa)^2[2(sina)^2+sina-1]=0
2(cosa)^2(sina+1)(2sina-1)=0
a属于(0,π/2),cosa>0 sina>0,因此只有sina-1/2=0 sina=1/2
tana=√3/3
sina=1/2 tana=√3/3