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# In mathematics, trigonometry, also called triangulation, is a branch of mathematics that studies relationships involving lengths and angles of triangles. The field emerged in the Hellenistic world during the 3rd century BC from applications of geometry to astronomical studies. Trigonometry is also the foundation of surveying.

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##### Alisa L.

University of Texas at Austin

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##### Ahyeon H.

University of California, Berkeley

##### Boris M.

University of North Carolina at Chapel Hill

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trig value for the co sign of negative three pi over four. Now, in order to do that, we need to find that co terminal angle of negative three pi over four. So it's because it is negative we're going thio at it to two pi over one, which is the same is two pi and reason we're adding to two pi. It's because that's 360 degrees and radiance. So let's find that common denominator. So we'll have the three pi over four because four is gonna be my common denominator, and that's gonna be eight pi over four. So when I subtract, that's gonna give me five pi over four. So once I find that co terminal angle at that point, I'm ready to find it on the circle. And I noticed that it is right here. Is that 5, 225 degrees, which is the degree measurement of five pi over four. We are looking for Kassian. So in an X Y cosign is our ex sign is our Why so Because we're doing that, we're looking for that X value. So the exact measurement is negative. Square root of two over to

Liberty University

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##### Alisa L.

University of Texas at Austin

AH
##### Ahyeon H.

University of California, Berkeley

##### Boris M.

University of North Carolina at Chapel Hill