One of the things we learned this week in Precalc 11 is how to use the cosine law to solve for angles or sidelengths of a triangle.
Cosine Law Formula
Since there are two laws, Sine and Cosine. To determine which law to use, look at one of the angles if there is one given, if the opposite side has a given sidelength then use the Sine Law, if the opposite side has an unknown sidelength then use the Cosine Law.
Solving for an angle
Solving for a sidelength
In △ABC, AB=7, ∠B=105°, and BC=10; determine side b to one decimal place.