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## Mathematics II (2018 edition)

### Course: Mathematics II (2018 edition)>Unit 10

Lesson 1: Pythagorean theorem

# Introduction to the Pythagorean theorem

Right triangles and the Pythagorean Theorem. Created by Sal Khan.

## Want to join the conversation?

• At , How is 144-36=112 ?? I thought it was 108!
• It is 108. Sal probably made a mistake. But honestly, he's human. He's a great man, yes, but he's human and humans make mistakes! It would be impossible to make 4000+ videos perfectly... :)
• I thought 144-36=108, or did I miss a step?
• Is there anything called normal triangle?
• I haven't heard of one. Generally you classify triangles as equilateral (all sides equal, all angles equal and maybe closest to "normal"), isosceles (2-sides equal, 2 angles equal) and scalene (all sides different all angles different).

You also classify them by acute (each angle is less than 90 degrees), right triangle (has one 90 degree angle) and obtuse (has one angle greater than 90 degrees)

When you get into Trigonometry, there are even more specific types of triangles
• Can an angle of a triangle ever equal 180 degrees?
• No, but it could get really close. for example, an isosceles triangle with angles .001, .001, and 179.998. You would not distinguish this triangle with a line since the angles are so small. The two equal sides would be slightly more than 1/2 of the other side.
• How do you find the length of the hypotenuse when only given one angle and the length of a side?
• i just want to be clear with myself... so can only a right triangle work with the Pythagorean theorem or can it work for other triangles too?
• It only works for right triangles. The law of cosines is a more general form that can work with any triangle.
• what if you get a left angle
• Can there be a right equilateral traingle?
• There cannot be a right equilateral triangle because "equilateral" means that all of the sides are the same measure. A right triangle has either 3 completely different sides (scalene) or two sides that are the same measure and one that is not (isoceles).
• At he said 112 but is 108 and didn't that change the rest of the formulae?
(1 vote)
• at sal said it was equal to 112 it is equal to 108 You may do the check if you want 36+108 is 144
• Well, yeah, I guess. But I think he was a little rushed.