- 5.2 | Verifying Trigonometric Identities
- 5.3 | Solving Trigonometric Equations
- 5.4 | Sum and Difference Formulas
- 5.5 | Multiple-Angle and Product-to-Sum Formulas
- 5.6 | Law of Sines

**Law of Cosines:**

$$

\begin{aligned}

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

b^2 & = a^2 + c^2 -2ac \cos B \\

c^2 & = a^2 + b^2 – 2ab \cos C

\end{aligned}

$$

**Heron’s Area Formula:**Given any triangle with sides of length \(a,b,\) and \(c,\) the area of the triangle is

$$

\text{Area} = \sqrt{s(s-a)(s-b)(s-c)}

$$

where \(s = (a+b+c)/2.\)