Use the identity for sin(A+B)\sin(A + B)sin(A+B) to express sin2A \sin 2A\,sin2A in terms of sinA \sin A\,sinA and cosA\cos AcosA.
Use the identity for cos(A+B)\cos(A + B)cos(A+B) to express cos2A \cos 2A\,cos2A in terms of sinA \sin A\,sinA and cosA\cos AcosA.
Hence express cos2A \cos 2A\,cos2A in terms of cosA \cos A\,cosA only.