<p>The answer is E, but how does that make any sense? Angle A = unknown and Angle C = 18...how can they just switch it around like that?</p>
<p><a href="http://i.imgur%5B/url%5D">http://i.imgur</a> .com/qywcwqn.png</p>
<p>What do you mean switch it around like that? All you do is use the law of cosines which is stated in the problem and solve for c, which involves taking the square root of the rest. It’s a relatively simple problem considering the law of cosines is given in the problem.</p>
<p>Just apply law of cosines</p>
<p>BC^2 = 12^2 + 18^2 - 2<em>12</em>18*cos 40°</p>