Answer:
Step-by-step explanation:
This is a Law of Sines problem. The expanded formula is
[tex]\frac{sinA}{a} =\frac{sinB}{b} =\frac{sinC}{c}[/tex] where the capital letters are the angles and the lowercase letters are the side lengths. We only use 2 of these ratios at a time. And in order to do that, we can only have one unknown per set of ratios. I have angle A and side a, so I'll use that ratio, but I don't have angle C to help me find side c. I also don't have angle B. But I do have side b, so I'll use the A and B sin stuff and then solve for C indirectly.
[tex]\frac{sin15}{9} =\frac{sinB}{12}[/tex] to solve for angle B. Cross multiply:
[tex]sinB=\frac{12sin15}{9}[/tex]
[tex]sinB=.3450926061[/tex] Use the inverse and sin keys on your calculator (in degree mode) to get that
B = 20.2°. Now that we have that, we can find the measure of angle C:
180 - 15 - 20.2 = 144.8°
Now we can use the sin ratio involving the angle C, side c (our unknown), and angle A and side a:
[tex]\frac{sin144.8}{c}=\frac{sin15}{9}[/tex] and cross multiply to solve for c:
[tex]c=\frac{9sin144.8}{sin15}[/tex] gives us that
c = 20.0
