bigzorro
幼苗
共回答了9个问题采纳率:88.9% 举报
1.
cos2a=3/5
sin2a=±4/5
sin4次方a+cos4次方a
=(sin^2 a+cos^2 a)^2-2sin^2 acos^2 a
=1-1/2 sin^2 2a
=1-1/2*16/25
=17/25
2.
(3sina+2cosa)(2sina-cosa)=0
tana=-2/3,or tana=1/2
a属于(-π/2 0)
∴tana=-2/3
sim2a=2tana/(1+tan^2 a)
=-12/13
cos2a=5/13
sin(2a+π/3)
=sin2acos(π/3)+cos2asin(π/3)
=-12/13*1/2+5/13*√3/2
=(5√3-12)/26
3.
分子=3(1-cosa)/2-sina+(1+cosa)/2
=2-(cosa+sina)=2-1/5=9/5
分母=tana+1/tana=(tan^2 a+1)/tana=2/sin2a
sina+cosa=1/5
(sina+cosa)^2=1/25
1+2sinacosa=1/25
sin2a=-24/25
原式=9/5*(-25/12)
=-15/4
实际上多次用到万能公式
1年前
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