已知sin(π-α)=2cos(π+α) 求sin(π-α)+5cos(2π-α)/3cos(π-α)-sin(-α)的值
已知tan(π-α)=2,求cos(α-π)tan(α-2π)tan(2π-α)/sin(π+α)的值
人气:316 ℃ 时间:2020-02-05 19:25:32
解答
sin(π-α)=2cos(π+α)
sina=-2cosa
tana=-2
[sin(π-α)+5cos(2π-α)]/[3cos(π-α)-sin(-α)]
=(sina+5cosa)/(-3cosa+sina) (上下同除以cosa)
=(tana+5)/(-3+tana)
=-3/5
tan(π-α)=2=-tana,
cos(α-π)tan(α-2π)tan(2π-α)/sin(π+α)
=-cosatanatana/(-sina)
=tana
=-2
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