A pentagram is a regular polygon that contains 10 isosceles triangles, and is used in golden ratio applications. Learn about the characteristics of a pentagram and its use as a religious symbol with help from a math teacher in this free video on basic math lessons.
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So what are some characteristics about the pentagram? Hi, I'm Jimmy Chang, and I've been teaching college math for nine years. And I'm sure you've seen a pentagram, but you may not know a lot about the background of the shape. So here are some highlights as to what the pentagram is and what it's used for. So the origins of the pentagram were in Ancient Greece and Babylonia. As you know, it is a symbol used a lot in the various religious faiths around us, and it is the simplest regular star polygon. Now, by a regular polygon, we're talking about a shape where all the sides are the same length around and, therefore, all the angles would be the same around. So if you take the pentagram in its simplest form, it is a regular polygon and all the parts are equal to each other. Now, within the pentagram are 10 isosceles triangles. Now, an isosceles triangle is a triangle in which two of the sides -- and, therefore, two of the angles -- are equal. Now, inside the pentagram are five acute triangles of which all the angles are less than 90 degrees each, and five obtuse triangles of which one of the angles of the triangle is greater than 90 degrees. And it's also used, lastly, in golden ratio applications. Now, the golden ratio is a number that was developed by the Greeks that's a number that's very close to 1.62. It's described as a visually pleasing ratio in that a lot of the shapes, like rectangles and such as cereal boxes and buildings, are built according to the golden ratio. Now, due to the 1.62 approximate value, inside the pentagram, the ratio of the longer edges to the shorter ones is approximately 1.62. So there are some characteristics about the pentagram. My name is Jimmy Chang.