Law of Sines

Law of Sines

Shiken premium Upgrade Banner

A Fresh Look at the Law of Sines and Its Practical Applications

Imagine this scenario: you are flying a kite that is 9 feet above the ground, while standing 12 feet away from the kite. Curious about the angle of elevation of your kite? Visualizing the situation, we can see that this forms a triangle, leading us to the Law of Sines.

Before we dive into the main topic, let's review the concept of triangle area. By connecting this concept with the Law of Sines and the Sine Ratio, we can see how these ideas work hand in hand. Just as a refresher, the Sine Ratio is determined by dividing the side opposite the angle by the hypotenuse of a right triangle.

Similarly, the area of a triangle can be found using the formula: Area = 1/2 x height x base. Now, let's examine the relationship between the Sine Ratio and triangle area. Consider this triangle:

  • A = 31o
  • b = 22
  • c = 18

Using the formula, we can calculate the area of this triangle to be approximately 101.98 cm2. But what if we have different information, like angle A and side b? In this case, we can use the Sine Ratio to determine the height (h) of the triangle, which can then be plugged into the area formula.

Now, let's tackle the Law of Sines. It is derived from our previous concepts, where all the area formulas for triangle ABC describe the same triangle. This means that the right side of these formulas are equal. By setting these areas equal to each other and simplifying, we arrive at the Law of Sines:

sin A/a = sin B/b = sin C/c

This means that for any triangle ABC, the ratio of the sine of an angle to the corresponding side length is equal to the other ratios.

The Law of Sines can be applied to a triangle if we know two things: the values of two angles and any side, or the values of two sides and an angle opposite one of them. Let's take a look at some examples of how we can use the Law of Sines to solve problems.


Example 1: Find the area of a triangle if A = 31o, b = 22 cm, and c = 18 cm.

Solution: Using the given formula, the area of this triangle is:
Area = 1/2 x b x c x sin A
= 1/2 x 22 x 18 x sin (31)
= 101.98 cm2 (rounded to two decimal places)

Example 2: Given the triangle below, find the value of angle B.


Explore More Subject Explanations

Try Shiken Premium
for Free

14-day free trial. Cancel anytime.
Get Started
Join 20,000+ learners worldwide.
The first 14 days are on us
96% of learners report x2 faster learning
Free hands-on onboarding & support
Cancel Anytime