sinX=4/5,x属于(0,π/2),cos(π-2X)等于多少
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sinX=4/5,x属于(0,π/2),cos(π-2X)等于多少
sinX=4/5,x属于(0,π/2),cos(π-2X)等于多少
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
sinx=4/5>sin45
45
cos(π-2X)=-cos2x=2sin^2x-1=7/25