Question

[(sin2α/1-cos2α)*(1-cosα/cosα)]*cot(α/2)

Answer 1

[(sin2α/1-cos2α)*(1-cosα/cosα)]*cot(α/2)

=[2sinαcosα/(sinα)^2*(1-cosα/cosα)]*cot(α/2)]

=[(1-cosα)/sinα]*(1+cosα)/sinα

=1

我是认为2倍啊?不是平方啊!

用倍角公式:

sin2α=2sinαcosα;

cos2α=1-(sinα)^2

半角公式:

cot(α/2)=(1+cosα)/sinα

转化就是答案