[질문] 미분 반각공식이랑 두배각공식좀

반각sin²α/2=1-cosα/2cos²α/2=1+cosα/2tan²α/2=(1-cosα)/(1+cosα)2배각rkrsin2A=2sinAcosAcos2A=cos2A-sin2A=1-2sin2A=2cos2A-1/tan2A=2tanA/(1-tan2A)