Question 987372
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Since you have two sides and the angle opposite one of those sides, you can use the Law of Sines.  Side AB is side c and side BC is side a.


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{c}{\sin{C}}\ =\ \frac{a}{\sin{A}]


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{10.9}{\sin(18.9)}\ =\ \frac{21.5}{\sin{A}]


Cross-multiply:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ 10.9\sin{A}\ =\ 21.5\sin(18.9)]


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \sin{A}\ =\ \frac{21.5\sin(18.9)}{10.9}]


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ A\ =\ \sin^{-1}\left(\frac{21.5\sin(18.9)}{10.9}\right)]


Make sure your calculator is set to degrees rather than radians.


John
*[tex \LARGE e^{i\pi}\ +\ 1\ =\ 0]
My calculator said it, I believe it, that settles it

*[tex \Large \ \
*[tex \LARGE \ \ \ \ \ \ \ \ \ \