9-3 & 9-4

We learned the law of sine and the law of cosine this. I think that the law of cosine is much easier to do because you basically just plug all of your work into the calculator. It is hard to learn what formulas to use with which triangles. There is also SOHCAHTOA. You cannot use the law of cosine on a right triangle. The only time you can use it is when you do not have any pairs on a non - right triangle. Most of these start off with a word problem where you have to draw your own triangle, so it can get a little tricky.

The formula for law of cosine is (oppleg)^2 = (adjleg)^2 + (adjleg^2) – 2(adj leg) (adj leg) cos (angle between)

Ex : Suppose 2 sides of a triangle have lengths of 10cm and 8 cm and the angle between them measures to be 140 degrees. Find the 3rd side. Once you draw your triangle, you plug the numbers into the formula. X^2 = 10^2 + 8^2 – 2 (8)(10)cos140 The first step is to get rid of the squared on the x, so you square root it.The next step is to put it in your calculator. X= 96.281 ends up being your answer.