For any △ ABC, let the lengths of the sides opposite angles A, B, and C be a, b, and c, respectively.
The Law of Sines relates the sine of each angle to the length of the opposite side.
sin A/a=sin B/b=sin C/c
We can find the third interior angle using the Triangle Angle Sum Theorem.
180- 18- 141= 21^(∘)
Consider the given triangle with new information.
We know that the length of a side is 13 and that the measure of its opposite angle is 21. We want to find the length of the side that is opposite to the angle whose measure is 141. We can use the Law of Sines again!
sin 21/13=sin 141/x
Let's solve the above equation for x using the Cross Product Property.
