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)_数学解答

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：398 ℃　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(...