In this blog, I will go over section 9-2, which involves the area of right and non-right triangles.
Formulas

-1/2 bh - only right triangles

-1/2 ab sin(angle between) - only for non-right triangles

Ex. Two sides of a triangle have lengths 7cm and 4cm. The angle between the siddes measures73 degrees. Find the area of the triangle.

A=1/2 ab sin(theta)
A=1/2(7)(4) sin73
A=14sin73
A=13.388 cm squared

Ex2 The area of triangle PQR is 15. p=5 and q=10. Find all possible measures of angle r.

first you have to draw a triangle. And then you have to label the sides bottom left point=P; top point=Q; bottom right point=R

15=1/2(5)(10) sin (theta)
15=25 sin (theta)
sin(theta)=15/25
(theta)=sin^-1(15/25)
(theta)=36.870 degrees

36.870 is in the first quadrant. Sin is positive in Q I and II.
-36.870+180=143.130 degrees.

So theta=36.870 degrees and 143.130 degrees.