When triangles are not right angle and we can no longer use SOH CAH TOA, one strategy is to use the Law of Sines.  However, when Law of Sines fails, we can turn to Law of Cosines.  This law works in two very specific examples.  When we are given all three sides and wish to solve an angle or is a triangle is sassy.  SAS.  This means we know two sides, AND we also know the angle that is BETWEEN those sides.  In either of these situations we would use the Law of Cosines to solve our triangle.

If you are unfamiliar with how to use the Law of Cosines, check out the video below and then find two sets of practice questions below which have you either solving for an unknown side or an unknown angle.

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Think you’ve got the hand of it?  In the next video I solve a Law of Cosines problem, but I make a mistake before I get to the end which causes the wrong answer to be obtained.  Try watching the video and see if you notice where the mistake is made before it gets to the end of the video.

If you were able to take care of these, feel free to check out the printable questions below which also have you drawing triangles and solving some word problems.