(Ⅰ)由题意得,f(x)=cosx?( 1 2 sinx+ 3 2 cosx)? 3 cos2x+ 3 4 = 1 2 sinx?cosx? 3 2 cos2x+ 3 4 = 1 4 sin2x? 3 4 (1+cos2x)+ 3 4 =