公式１．１(相互関係)
(1) tanθ = \frac{sinθ}{cosθ} , sin^2θ+cos^2θ = 1 , 1 + tan^2θ = \frac{1}{cos^2θ}
(2) sin(-θ) = -sinθ , cos(-θ) = cosθ , tan(-θ) = -tanθ
(3) sin(θ + 2nπ) = sinθ , cos(θ + 2nπ) = cosθ , (nは整数)
(4) sin(θ + π) = -sinθ , cos(θ + π) = -cosθ , tan(θ + π) = tanθ
(5) sin(θ + \frac{π}{2}) = cosθ , cos(θ + \frac{π}{2}) = -sinθ , tan(θ +\frac{π}{2}) = - \frac{1}{tanθ}
