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问题: p46

10.证明
1.tana/2=sina/1+cosa=1-cosa/sina

解答:

sina/(1+cosa)
=2sin(a/2)cos(a/2)/[1+2cos²(a/2)-1]
=2sin(a/2)cos(a/2)/2cos²(a/2)
=sin(a/2)/cos(a/2)/
=tan(a/2)

(1-cosa)/sina
={1-(1-2sin²(a/2)]}/2sin(a/2)cos(a/2)
=2sin²(a/2)]}/2sin(a/2)cos(a/2)
=sin(a/2)/cos(a/2)/
=tan(a/2)