已知sin(x+30)=1/3 求cos(120-2x)_数学解答

已知sin(x+30)=1/3 求cos(120-2x)

人气：246 ℃　时间：2020-04-10 05:33:00

解答

cos(2x+60)
=cos[2(x+30)]
=1-2sin²(x+30)
=7/9
cos(120-2x)
=cos[180-(2x+60)]
=-cos(2x+60)
=-7/9