Trigonometry Workbook For Dummies
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All functions, including trig functions, can be described as being even, odd, or neither. Knowing whether a trig function is even or odd can help you simplify an expression. These even-odd identities are helpful when you have an expression where the variable inside the trig function is negative (such as –x). The even-odd identities are as follows:

sin(–x) = –sinx csc(–x) = –cscx
cos(–x) = cosx sec(–x) = secx
tan(–x) = –tanx cot(–x) = –cotx

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Mary Jane Sterling taught algebra, business calculus, geometry, and finite mathematics at Bradley University in Peoria, Illinois, for more than 30 years. She is the author of several For Dummies books, including Algebra Workbook For Dummies, Algebra II For Dummies, and Algebra II Workbook For Dummies.

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