Trigo Question help!?
2015-09-06 6:21 am
can someone guide me in solving this question sin 4x+sin2x=cos x( for the range x is equal to 0 smaller and equal to x and 2 pie is bigger and equal to 0.)
回答 (1)
2015-09-06 12:24 pm
✔ 最佳答案
Suppose the range you mean is 0 ≦ x < 2πsin 4x + sin 2x = cos x
2 * sin (4x+2x)/2 * cos (4x-2x)/2 = cosx
2 * sin 3x * cos x = cos x
cos x ( 1 - 2 sin 3x ) = 0
cos x = 0 or sin 3x = 1/2
cos x = 0
x = π/2 or 3π/2
sin 3x = 1/2 and 0 ≦ 3x < 6π
3x = π/6 , 5π/6 , 13π/6 , 17π/6 , 25π/6 , 29π/6
x = π/18 , 5π/18 , 13π/18 , 17π/18 , 25π/18 , 29π/18
Ans: x = π/2 , 3π/2 , π/18 , 5π/18 , 13π/18 , 17π/18 , 25π/18 , 29π/18
收錄日期: 2021-05-02 14:11:24
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https://hk.answers.yahoo.com/question/index?qid=20150905222136AA756VZ