Question

Let f(x)=x2 and g(x)=sinx for all x∈R .Then the set of all x satisfying (fogogof)(x)=(gogof)(x) where fog(x)=f(g(x)) is (a)±nπ−−−√;n∈{0,1,2}(b)±nπ−−−√;n∈{1,2}(c)π2+2nπ;n∈{...−2,−1,0,1,2}(d)2nπ;n∈{...−2,−1,0,1,2...} Why not n=0