已知sina-2cosa=0 sin2a+sinacosa+3cos2a ( sin2a+sinacosa)/(sin2a+1) (sina+3cosa)/(2sina+5cosa)

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已知sina-2cosa=0 sin2a+sinacosa+3cos2a ( sin2a+sinacosa)/(sin2a+1) (sina+3cosa)/(2sina+5cosa)
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已知sina-2cosa=0 sin2a+sinacosa+3cos2a ( sin2a+sinacosa)/(sin2a+1) (sina+3cosa)/(2sina+5cosa)
已知sina-2cosa=0
sin2a+sinacosa+3cos2a ( sin2a+sinacosa)/(sin2a+1) (sina+3cosa)/(2sina+5cosa)

已知sina-2cosa=0 sin2a+sinacosa+3cos2a ( sin2a+sinacosa)/(sin2a+1) (sina+3cosa)/(2sina+5cosa)
∵sina-2cosa=0,则sina=2cosa ∴tana=2,sina=4/5,cosa=1/5 ∴①sin2a+sinacosa+3cos2a=2sinacosa+sinacosa+3(2cosa-1)=3sinacosa+6cosa-3=12cosa-3=-3/5 ②( sin2a+sinacosa)/(sin2a+1)=3sinacosa/(sina+2sinacosa+cosa)=3tana/(tana+2tana+1)=2/3 ③(sina+3cosa)/(2sina+5cosa)=(tana+3)/(2tana+5)=5/9