已知x属于(0,π/20),求函数y=cos(π/12-x)-cos(5π/12+x)的值域是
问题描述：
已知x属于(0,π/20),求函数y=cos(π/12-x)-cos(5π/12+x)的值域是
答
y=cos(π/12-x)-cos(5π/12+x)
=cos(π/12-x)-cos[π/2-(π/12-x)]
=cos(π/12-x)-sin(π/12-x)
=√2sin[π/4-(π/12-x)]
=√2sin(π/6+x)
值域是[-√2,√2]