After learning about the nice, simple Law of Sines yesterday we have since moved forth to the not as simple Law of Cosines.

Use the Law of Cosines when you are given

1) three sides (SSS)

2) two sides and the included angle (SAS)

The Laws of Cosines can be written in several different forms (as seen below), depending on which angles or sides you desire to solve:

-----Don't forget to take the inverse cosine once you've solved the right side-----

If you notice the pattern within these formulas it will make remembering them much easier. The side which you are trying to find is that which is subtracted in the numerator, and the denominator contains the other two sides.

In addition to the laws of cosines we learned about Heron's Formula, which allows you to find the area of an oblique triangle:



s, in this case, represents the semi-perimeter (that being one-half of the total perimeter of the triangle).


Hopefully this provides sufficient information to get you going but you may refer back to section 6.2 in your book.



Damien Hirst