2.(2023•青羊区校级模拟)已知函数f(x)=aln(x−π4)+sinxf(x)=aln(x-\frac{\pi }{4})+\sin xf(x)=aln(x−4π)+sinx,其中aaa为实数.(1)若f(x)f(x)f(x)在区间(π4,3π4)(\frac{\pi }{4},\frac{3\pi }{4})(4π,43π)上单调递增,求aaa的取值范围;(2)求证:对任意的实数aaa,方程f(x)=cosxf(x)=\cos xf(x)=cosx均有解.