三角比

trigonometric ratio

三角比についての恒等式

$ \frac{\sin θ}{\cos θ} = \tan θ

$ \sin^2 θ + \cos^2 θ = 1

$ \frac{1}{\cos^2 θ} = 1 + \frac{\sin^2 θ}{\cos^2 θ}

余角: complimentary angle

$ \sin\left( \frac{π}{2} - θ\right) = \cos θ

$ \cos\left( \frac{π}{2} - θ\right) = \sin θ

$ \tan\left( \frac{π}{2} - θ\right) = \frac{1}{\tan θ}

$ a^2 = b^2 + c^2 - 2bc\cos A

$ c\sin B = b\sin C

$ \frac{a}{\sin A} = \frac{b}{\sin B} = \frac{c}{\sin C}