求证sina^2+sin&^2-sina^2*sin&^2+cosa^2*cos&^2=1

求证sina^2+sin&^2-sina^2*sin&^2+cosa^2*cos&^2=1
求证sina^2+sin&^2-sina^2*sin&^2+cosa^2*cos&^2=1

求证sina^2+sin&^2-sina^2*sin&^2+cosa^2*cos&^2=1
原式=sina^2+(sin&^2-sina^2*sin&^2)+cosa^2*cos&^2
=sina^2+sin&^2(1-sina^2)+cosa^2*cos&^2
=sina^2+(sin&^2*cosa^2+cosa^2*cos&^2)
=sina^2+(sin&^2+cos&^2)*cosa^2
=sina^2+cosa^2
=1

(sina)^2+(sin&)^2-(sina)^2*(sin&)^2+(cosa)^2*(cos&)^2
=(sina)^2) + (sin&)^2(1-(sina)^2) + (cosa)^2(cos&)^2)
=(sina)^2 + (sin&)^2(cosa)^2 + (cosa)^2(cos&)^2
=(sina)^2 + (cosa)^2
=1.

sina=sin[(a＋b)/2＋(a－b)/2]=sin(a＋b)/2cos(a－b)/2＋cos(a＋b)/2sin(a－b)/2 sinb=sin[(a＋b)/2－(a－b)/2]=sin(a＋b)/