cos(1/7pi)*cos(2/7pi)*cos(3/7pi)=-cos(1/7pi)*cos(2/7pi)*cos(4/7pi)=-4sin(1/7pi)*cos(1/7pi)*cos(2/7pi)*cos(4/7pi)/4sin(1/7pi)=-2sin(2/7pi)cos(2/7pi)*cos(4/7pi)/4sin(1/7pi)=-sin(4/7pi)cos(4/7pi)/4sin(1/...