[PDF] 8 6 practice law of cosines

When to use the law of cosines?

When to Use. The Law of Cosines is useful for finding: the third side of a triangle when we know two sides and the angle between them (like the example above) the angles of a triangle when we know all three sides (as in the following example)

How many angles do you need to solve a cosine equation?

The four parts are three sides and one angle. So you either need 2 sides and an angle to solve for the remaining side or all three sides to solve for an angle. So if you know two angles (which lets you figure out the third so technically three angles) and a side you can't just use the law of cosines.

What mnemonics do you need to memorize the law of cosines?

For the Law of Cosines, all you really need to memorize is the "-2bc*cos ?" part. The rest of the Law of Cosines is just the Pythagorean Theorem. I'm not sure if that counts as a mnemonic, but it is a way to cut down how much you have to memorize. Show more...

What is 12 times 9 times the cosine of 87 degrees?

Minus two times 12 times nine, times the cosine of 87 degrees. And this is going to be equal to, let's see, this is 225 minus, let's see, 12 times nine is 108. 108 times two is 216. Minus 216 times the cosine of 87 degrees. Now, let's get our calculator out in order to approximate this.