Cos is short for Cosine ( Complementary Sine)
Similrly
Sin is short for Sine
Tan is short for Tangent.
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This can be done on a graphing calculator by making sure you have your calculator in degrees mode, and then tentering the cos(23). You get an answer of 0.9205048535.
Things
Any calculator sold as a "scientific calculator" has the basic trigonometric functions (sin, cos, tan) and the inverse trigonometric functions (arc-sin, arc-cos, arc-tan). That's about all you need.You can also use the calculator that comes on your computer - for example, in Windows, press Windows-R, and then type "calc". You may have to change the calculator mode, to "scientific calculator". Yet another option is a spreadsheet, for example, Excel. Note that in Excel, angles are expressed in radians; if you want degrees, you also need the special functions to convert degrees to radians, or radians to degrees. However, if you want to do your homework while you are NOT at your computer, you are better off buying a calculator.
Look for a button marked "cos". Note that some calculators have degrees, radians and other measurements. So check you are in the right mode.
cos(30)cos(55)+sin(30)sin(55)=cos(30-55) = cos(-25)=cos(25) Note: cos(a)=cos(-a) for any angle 'a'. cos(a)cos(b)+sin(a)sin(b)=cos(a-b) for any 'a' and 'b'.