9-3 is all about the Law of Sines. The law of sine is only used with NON-RIGHT TRIANGLES. You are only about to use the law of sines when you have an angle and an opposite leg value that you know.

Example: An engineer wants to determine the distances from points A to B to a inacessible point C. From direct measurement the engineer knows the AB=25cm AngleA=110° AngleB=20°. Find AC&BC

a.You draw out your triangle from what you already know. Once draw you see the you do not know legs a or b and AngleC.
b. To find angle c subtract the two angles known by 180°.
180-110-25=50°
c.Plug into formula..
sin50/25=sin110/AC
d.Cross multiply to get BCsin50=25sin10
e.Get BC by itself by dividing 50.
f. Answer for angle BC is 25sin110/sin50 which equals 30.667
-Next solve or AC-
a.ACsin50=25sin20
b.Divide to get AC alone.
c.Answer is 25sin20/sin50 which equals 11.162