For this 150 words, I will be reviewing section 9-4, Law of Cosines. You use this when you don't have a pair for Law of Sines. B-Rob told us to only use this formula for a LAST resort because its complicated and leaves more room for mistakes.
Here's the formula:
(opp leg)^2=(adj leg)^2+(adj leg)^2-2(adj leg)(adj leg)cos(angle b/w)
you can plug in for any part of this formula and solve.
Ex. you have a triangle with side lengths of 3 and 7 with an angle between that measures 130 degrees. Find the third side.
the first thing you always do is draw out your triangle, then you can see that you cannot use sohcahtoa because it has no information that would lead to it being a right triangle, so you check for law of sines, there isn't a pair for you to use, so you turn to your last resort, law of cosines
you plug in your fomula
you get x^2=3^2(7^2)-2(3)(7)cos(130)
type that in your handy dandy calculator and you got it!
X=9.22 and if they give you units, you would indicate your answer
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