46/91*46/91+45/91*45/91-46/91*45/91-45/91*44/91
＝（46/91）^2+(45/91)^2-46/91*45/91+46/91*45/91-46/91*45/91-45/91*44/91
=(46/91-45/91)^2+46/91*45/91-45/91*44/91
=(1/91)^2+[45*(46-44)]/91*91
=1/91*91+90/91*91
=91/91*91
=1/91