[질문] 삼각함수sec가뭐야?? 삼각함수여러가지공식좀

secθ= 1/cosθ 1)sinA+sinB=2cosA+B/2*sinA-B/2 2)sinA-sinB=2sinA+B/2*cosA-B/2 3)cosA+cosB=2CosA+B/2*cosA-B/2 4)cosA-cosB=-2SinA+B/2*sinA-B/2