中考数学辅导：三倍角公式推导
三倍角公式推导
tan3=sin3/cosplay3
=/
=+cosplay^2sin-sin^3)/-cosplaysin^2-2sin^2cosplay)
上下同除以cosplay^3，得：
tan3=)/)
sin3=sin=sin2cosplay+cosplay2sin
=2sincosplay^2+)sin
=2sin-2sin^3+sin-2sin^3=3sin-4sin^3
cosplay3=cosplay=cosplay2cosplay-sin2sin
=-1)cosplay-2cosplaysin^2
=2cosplay^3-cosplay+)
=4cosplay^3-3cosplay
即
sin3=3sin-4sin^3
cosplay3=4cosplay^3-3cosplay
