Question

为什么sinA=[2tana/2]/1 tana/2*tana/2

Answer 1

sina=2sin(a/2)cos(a/2)

=[2sin(a/2)cos(a/2)/cos²(a/2)]/[1/cos²(a/2)]

=2tan(a/2)/{[(sin²(a/2)+cos²(a/2)]/cos²(a/2)}

=2tan(a/2)/[tan²(a/2)+1]