How can we find the area of the triangle with 3 given sides? In this geometry tutorial, we will see how to use Heron's formula to find the area of the triangle whose sides are 11, 13, and 20. Note that this is also a "Heronian triangle" because both its sides and area are positive whole numbers. We will also learn the proof of the formula.
Heron's formula proof (no law of cosine) https://www.youtube.com/watch?v=9qbpmYqr4so
Law of sin and cosine proof: https://www.youtube.com/watch?v=843Uw-Hj-OQ
0:00 Finding the area of the triangle whose sides are 10, 13, and 20
2:55 Why this isn't a right triangle
4:41 Proof of the Heron's formula
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