tan(x+四分之派)=负二分之一求cos2x的值
人气：275 ℃ 时间：2020-06-02 19:35:27
解答
tan(x+四分之派)=-1/2
（tanx+1）/（1-tanx）=-1/2
2（tanx+1）=tanx-1
tanx=-3
cos²x=1/sec²x=1/（tan²x+1）=1/10
cos2x=2cos²x-1=-4/5
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