公式的推导,谁来帮我～····万能公式:sinx=2tg(x/2)/(1+tg(x/2)^2)cosx=(1-tg(x/2)^2)/(1+tg(x/2)^2)tgx=2tg(x/2)/(1-tg(x/2)^2)怎么推导的?

Question

公式的推导,谁来帮我～····
万能公式:
sinx=2tg(x/2)/(1+tg(x/2)^2)
cosx=(1-tg(x/2)^2)/(1+tg(x/2)^2)
tgx=2tg(x/2)/(1-tg(x/2)^2)
怎么推导的?

Answer 1

sinx=2sin(x/2)cos(x/2)/1...1=[sin(x/2)^2+cos(x/2)^2]
cosx=[cos(x/2)^2-sin(x/2)^2]/1..
代入化简可得.