nickman88
幼苗
共回答了24个问题采纳率:79.2% 举报
已知3sina-2cos=o
3sina=2cosa
sina/cosa=2/3
(1)(cosa-sina)/(cosa+sina)
=(1-sina/cosa)/(1+sina/cosa)
=(1-2/3)/(1+2/3)
=1/3 / (5/3)
=1/5
(2)sin^2a-2sinacosa+4cos^2a
=(sin^2a-2sinacosa+4cos^2a)/(sin^2a+cos^2a)
=((sina/cosa)^2-2sina/cosa+3)/((sina/cosa)^2+1)
=((2/3)^2-2*2/3+3)/((2/3)^2+1)
=(4/9-4/3+3)/(4/9+1)
=(4-12+27)/(4+9)
=19/13
1年前
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