This week we talked about sine and cosine law in order to help find the missing side length or angle.

Though there are only sometimes you can use sine law, and when you cannot is when you can use cosine law.

You only use sine law when you have an angle and a side length across from each other and another number. Each corner or side of the triangle is either labeled by a lower case letter or an upper case. The upper case letters are the angles and the lower case letters are the sides. The sides across from an angle are labeled the same letter but in lower case.

This is how you label the triangle and an example of when you can use sine law:

These are the formulas for sine law, the one on top is to find the side length, and the bottom is to find an angle. Though you only need two of the three fractions out of the formula, one with all information inserted, and the other with one of the variables filled in. Depending on the information you are trying to find will decide if you will insert a degree or a side length into the equation.

After inserting all the information necessary, this is an example of how you work through and solve with sine law when trying to find a side length.

This is an example when you are trying to find an angle.

Cosine Law works very similarly; insert the correct information, use one of the two formulas for either finding a side length or an angle and work through the problem.

This is an example of a question where you will need to use the cosine law.

These are the formulas for cosine law.

This is an example of finding a side length.

This is an example of finding an angle.