Cosine Law

For any triangle:

The following is true:

$$ c^2 = a^2 + b^2 - 2 \cdot a \cdot b \cdot \cos(\theta) $$

Note that the naming of the sides and angle is arbitrary. The formula is true as long as \(\small \theta\) is the angle opposite side c.

Sources #

• Wikipedia
• Byju’s