sina^2*sinb^2+cosa^2*cosb^2-(cos2a*cos2b)/2求解 答案是1/2
网友回答
sina^2*sinb^2+cosa^2*cosb^2-(cos2a*cos2b)/2
= sina^2*sinb^2+(1- sina^2)(1- sinb^2)-(1-2 sina^2)(1-2 sinb^2)/2
= sina^2*sinb^2+[1- sina^2- sinb^2+ sina^2*sinb^2]
-[1- 2sina^2- 2sinb^2+ 4sina^2*sinb^2] /2
= sina^2*sinb^2+[1- sina^2- sinb^2+ sina^2*sinb^2]
-[1/2- sina^2- sinb^2+2sina^2*sinb^2]
=[1- sina^2- sinb^2+ 2sina^2*sinb^2]
-[1/2- sina^2- sinb^2+2sina^2*sinb^2]
=1/2