cos(x-y)=,cos(x-y)

cos(x y)/1-cos(x y)=-1 1/1-cos(x y)是怎么算的?
求函数y=cos05x-4x 2的最大值及最小值
sin(x y)和cos(x y)等式的几何原理图示
当x,y∈[0,π]时,如何计算cosxcosycos(x-y)的范围?
y=sin(x)和y=cos(x)合影