Identify the length of two adjacent sides of a triangle and the measure of the respective angle at their intersection point. For example, assume a triangle has two adjacent sides measuring 3 and 4 inches respectively and form an angle measuring 45 degrees.
Substitute the observed values into the area formula for a triangle. Area = 1/2 (a)*(b)*sin(c), where a and b are the lengths of the two sides and c is the measure of the angle.
Plug the equation into a scientific calculator to identify the area of the triangle. In the example problem, plugging the values into a calculator results in an area of 4.2 square inches: 1/2*(4)*(3)* sin(45) = 4.2 inches^2.