求函数y=log以1/3为底[cos(x/3+π/4)]的增区间

函数y=log以1/3为底[cos(x/3+π/4)]的增区间因为函数y=log以1/3为底,本身就是一个减函数所以函数y=log以1/3为底[cos(x/3+π/4)]的增区间就是cos(x/3+π/4)的减区间,又因为cos(x/3+π/4)>0kπ大于等于x/3+π/4小于π/2+kπ所以3kπ-3π/4大于等于x小于3π/4+3kπ