malorie's blog

9-3 Law of Sines

In order to do law of sines there must be a right angle and there must be an angle with an opposite to use the formula.

Formula:

sin(angle)/ opposite leg = sin(angle 2) opposite leg 2

Example:

in the triangle ABC, angle B= 126, b=12, c=7. Determine if angle C exsist. Find all possible measures of angle C.

sin126/12= sin C/7

126 is oppisite to 12
you would use sinC because C is the angle you are looking for, and 7 is opposite of it.

12 sin C = 7 sin 126 (Cross Multply)

divide by 12 to get sin C by itself.

take the inverse of sin C.

C=28.159

you have to find all values of C so you would find the second quadrant angle becaue sin is positive in the first and second quadrant.

you get 151.841 which isn't reasonable so you don't use it.

your final answer is C= 28.159



Example 2:

Solve the triangle ABC. Angle C= 25, c=2, and b=3.

sin25/2= sinB/3
cross multiply
divide by 2
take the inverse
B=39.3


A= 115.7

sin25/2= sin 115.7/a
cross multiply
divide by sin25
solve



It's that simple (:
a=4.26