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已知tan(a+π/4)=-1/2,π/2
人气:406 ℃ 时间:2020-02-05 10:14:12
解答
tan(a+π/4)=-1/2-->tana=-3-->cosa=-√10/10
(sin2a-2cos^2a)/sin(a-π/4)=(2sinacosa-2cos^2a)/sin(a-π/4)
2cosa(sina-cosa)/sin(a-π/4)
=2√2cosa=-2√5/5
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