The thing I understood most this week was section 9 – 3, Law of sines. The law of sines can only be used with non –right triangles. The only time you can use law of sines is when you have or are given one side, and one angle that are opposites of each other. This is the thing that you try before you use the law of cosines.
The formula is (sin (angle) / opposite leg) = (sin (angle 2) / opposite leg)
To solve the formula you have to cross multiply.
Example 1:
Triangle ABC, angle B = 120 degrees, b = 10, c = 8.
Sin ( 120 degrees ) / 10 = sin(C) / 8
10sin ( C ) = 8 sin( 120 degrees )
10 sin ( C ) = 6.928
Sin ( C ) = 6.928 / 10
C = Sin^ -1 ( 6.928 / 10 )
C = 43.8522 degrees