# Intro Tl;dr, the law of sines is: $$ \frac{\sin(\alpha)}{a} = \frac{\sin(\beta)}{b} = \frac{\sin(\gamma)}{c} $$ Under convention: - Angle $\alpha$ is opposite side $a$ - Angle $\beta$ is opposite side $b$ - Angle $\gamma$ is opposite side $c$ - Any triangle that is *not a right triangle* is called an oblique triangle. There are two types of oblique triangles: - **Acute triangles**: This is an oblique triangle where all three interior angles are less than $90\degree$ or $\dfrac{\pi}{2}$ radians. - **Obtuse Triangle**: This is an oblique triangle where one of the interior angles is greater than $90\degree$. ## Different types of oblique triangles 1. **ASA Triangle**: (Angle Side Angle) - We know the measurements of two angles and the side between them 2. **AAS**: We know the measurements of two angles and a side that is not between the known angles. 3. **SSA**: We know the measurements of two sides and an angle that is not between the known sides. These triangles can be solved by adding a line that goes from one vertex to intersect perpendicular to the opposite side, forming two right triangles ($h$). ## Solving for the law of sines We know that $\sin\alpha = \dfrac{h}{b}$ and $\sin\beta = \dfrac{h}{a}$. We can sole both equations for $h$ to get: - $h = b\sin\alpha$ - $h = a\sin\beta$ Setting both equations equal to each other gives us: $b\sin\alpha = a\sin\beta$ Multiply both sides by $\dfrac{1}{ab}$ gives yields $\dfrac{\sin\alpha}{a} = \dfrac{\sin\beta}{b}$ # SSA triangles Side side angle triangles may be solved to have one possible solution, two possible solutions, or no possible solutions. - No triangle: $a < h$ - One triangle: $a \ge b$ - Two triangles: $h < a < b$ - One right triangle: $a = h$