sinX=4/5,x属于(0,π/2),cos(π-2X)等于多少

问题描述:

sinX=4/5,x属于(0,π/2),cos(π-2X)等于多少

x属于(0,π/2)
sinx=4/5 >sin(π/4)=根号2/2
所以x>π/4
π/2