tanα=m(3π/2
问题描述：
tanα=m(3π/2
答
cosα=1/sqrt(m^2+1)=sqrt(m^2+1)/(m^2+1)
【sqrt表示根号】
答
(tanα)^2+1=(secα)^2
secα*cosα=1 cosα=±1/√((tanα)^2+1)
因为3π/20
cosα=1/√((tanα)^2+1)=c1/√(m^2+1)
答
tana=sina/cosa
sin²a+cos²a=1
联立二者,得（m²+1）cos²a=1
cosa=1/根号（m²+1）=根号（m²+1）/m²+1
OK了.
答
3π/20
cosα=1/√[1+(tanα)^2]
cosα= 1/√(m^2+1)