sinX=1/3 ,cos(2X - π)=

问题描述:

sinX=1/3 ,cos(2X - π)=

cos(2x- π)= cos 2(x-π/2)=2*【cos(x-π/2) 】^2 -1 = 2 * (sin x )^2 -1 = - 7/9.