已知COS(X+派/4)=根号2/10,x属于(派/2,3派/4) 求sinx 求sin(2x+派\4)
人气:439 ℃ 时间:2019-08-18 17:17:01
解答
x属于(派/2,3派/4),X+派/4属于(3派/4,派),所以sin(X+派/4)=7√2/10.Sinx=sin[(X+派/4)- 派/4]= sin(X+派/4)cos派/4-cos(X+派/4)sin派/4=3/5.所以cosx=-4/5.sin(2x+派/4) =sin[(X+派/4)+x]= sin(X+派/4)cosx+cos(...
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