Consider the right triangle shown below.
We shall discuss two methods for solving the right triangle.
Method 1. Use of trigonometric ratios
To use trigonometric ratios requires that either m∠A or m∠B is known and that one of the sides a, b, or c is known.
Example:
Assume that m∠A is known, then m∠B = 90° - m∠A.
Also, assume that b is known.
By definition,
tan A = a/b => a = b*tan A
cos A = b/c => c = b/cos A, or
sin A = a/c => c = a/sin A
Method 2. Algebraic method
When neither m∠A nor m∠B is known, then it is necessary to know the values of two sides: (a and b), (a and c), or (b and c).
The Pythagorean theorem states that
a² + b² = c²
(a) If a and b are known, then
c = √(a² + b²)
(b) If a and c are known, then
b = √(c² - a² )
(c) If b and c are known, then
a = √(c² - b²)
Once all sides are known, trigonometric ratios can be used t determine m∠A and m∠B.
Example:
Because a and c are known,
sin A = a/c
A = sin⁻¹ (a/c), which can be determined from the calculator.
