What Is the Unit Circle?

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In math, the unit circle is used in trigonometry to relate trigonometric ratios. Discover the definition of the unit circle in math with tips from a mathematics tutor in this free video on math lessons.

Part of the Video Series: Math Definitions
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Video Transcript

The unit circle is used in trigonometry to relate the trigonometric ratios. Let me illustrate. Here's a unit circle, whose radius is equal to one. Radius equal to one, and this is called a standard precision, where, where you have the, where you have the angle, starting off from the x axis. So, the, the first line is called the initial side, and where the triangle ends is called the terminal side. And, as I mentioned before, the standard position is where the triangle starts, with the positive x axis. Now, to find the lengths of the adjacent side, and the opposite side, you project, this point on the circle, down to the axis. So, this, I mentioned is the adjacent side, than you project this to the x, y axis, and this dimension is the opposite. Oops, opposite. So then, sin of theta is the ratio of, let me "wri", label this, hypotenuse. Sin is the opposite of the hypotenuse. Co-sin theta is adjacent of the hypotenuse, and the tangent of theta is opposite of the adjacent.


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