Question

(sinA+sinB)/(cos A +cos B) =tan (A+B)/2 怎么证明?

Answer 1

(sinA+sinB)/(cos A +cos B)

=2sin(A+B)/2*cos(A-B)/cos2/cos(A+B)/2*cosA-B)/2

=sin(A+B)/2/cos(A+B)/2

=tan (A+B)/2

用和差化积公式