co·​sine | \ ˈkō-ˌsīn How to pronounce cosine (audio) \

Definition of cosine

1 : a trigonometric function that for an acute angle is the ratio between the leg adjacent to the angle when it is considered part of a right triangle and the hypotenuse
2 : a trigonometric function cos θ that for all real numbers θ is given by the sum of the alternating series {latex}1 - \frac{x^2}{2!} + \frac{x^4}{4!} - \frac{x^6}{6!} + \frac{x^8}{8!} - \dots{/latex} and that is exactly equal to the cosine of an angle of measure θ in radians

Examples of cosine in a Sentence

Recent Examples on the Web Since the cosine of 180 degrees is negative 1, the work done by this force is -0.11 Joules. Rhett Allain, WIRED, "Even Physics Textbooks Tend to Get Friction Slightly Wrong," 16 Aug. 2019 The link was so clear it could be described in derivative sines and cosines, mathematical concepts taught in college trigonometry. Brandon Keim, WIRED, "More Evidence Found for Quantum Physics in Photosynthesis," 6 Dec. 2011

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'cosine.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of cosine

1635, in the meaning defined at sense 1

History and Etymology for cosine

New Latin cosinus, from co- + Medieval Latin sinus sine

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Time Traveler for cosine

Time Traveler

The first known use of cosine was in 1635

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Cite this Entry

“Cosine.” Dictionary, Merriam-Webster, Accessed 3 Jul. 2020.

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How to pronounce cosine (audio)

English Language Learners Definition of cosine

geometry : the ratio between the long side (called the hypotenuse) and the side that is next to an acute angle in a right triangle

More from Merriam-Webster on cosine

Britannica English: Translation of cosine for Arabic Speakers Encyclopedia article about cosine

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