求证:cotα-cot2α=csc2α

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求证:cotα-cot2α=csc2α
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求证:cotα-cot2α=csc2α
求证:cotα-cot2α=csc2α

求证:cotα-cot2α=csc2α
cotα-cot2α
=cosα/sinα-cos2α/sin2α
=cosα/sinα-cos2α/(2sinαcosα)
=2(cosα)^2/(2sinαcosα)-cos2α/(2sinαcosα)
=[2(cosα)^2-cos2α]/(2sinαcosα)
=[2(cosα)^2-(cosα)^2+(sinα)^2]/(2sinαcosα)
=[(cosα)^2+(sinα)^2]/(2sinαcosα)
=1/(2sinαcosα)
=1/sin2α
=csc2α

?csc是?汗

=cosa/sina-cos2a/sin2a
=cosa/sina-(cos^2a-sin^2a)/2sinacosa
=cosa/2sina+sina/2cosa
=1/2sinacosa
=1/sin2a
=cSc2a
a代替了啊尔发