作业帮三角比：[cos(4a-PAI/2)*sin(PAI/2-2a)]/[(1+cos2a)*(1+cos4a)]
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三角比：[cos(4a-PAI/2)*sin(PAI/2-2a)]/[(1+cos2a)*(1+cos4a)]
[cos(4a-π/2)*sin(π/2-2a)]/[(1+cos2a)*(1+cos4a)]
=[cos(π/2-4a)*sin(π/2-2a)]/[(1+cos2a)*(1+cos4a)]
=(sin4a*cos2a)/[(1+cos2a)*(1+cos4a)]
=(sin4a*cos2a)/{(1+cos2a)*[1+2(cos2a)^2-1]}
=(sin4a*cos2a)/{(1+cos2a)*2(cos2a)^2}
=sin4a/{(1+cos2a)*2cos2a}
=2sin2a*cos2a/{(1+cos2a)*2cos2a}
=sin2a/(1+cos2a)
=tana
=[cos(π/2-4a)*sin(π/2-2a)]/[(1+cos2a)*(1+cos4a)]
=(sin4a*cos2a)/[(1+cos2a)*(1+cos4a)]
=(sin4a*cos2a)/{(1+cos2a)*[1+2(cos2a)^2-1]}
=(sin4a*cos2a)/{(1+cos2a)*2(cos2a)^2}
=sin4a/{(1+cos2a)*2cos2a}
=2sin2a*cos2a/{(1+cos2a)*2cos2a}
=sin2a/(1+cos2a)
=tana
三角比：[cos(4a-PAI/2)*sin(PAI/2-2a)]/[(1+cos2a)*(1+cos4a)]
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