If f(-x) = f(x) for all x then x is even. Example f(x) = cos(x).
If f(-x) = -f(x) for all x then x is odd. Example f(x) = sin(x).
In all other cases, f(x) is neither.
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Looking at the graph of the function can give you a good idea. However, to actually prove that it is even or odd may be more complicated. Using the definition of "even" and "odd", for an even function, you have to prove that f(x) = f(-x) for all values of "x"; and for an odd function, you have to prove that f(x) = -f(-x) for all values of "x".
Basically, a knowledge of even and odd functions can simplify certain calculations. One place where they frequently appear is when using trigonometric functions - for example, the sine function is odd, while the cosine function is even.
An even function is symmetric around the vertical axis. An odd function - such as the sine function - has a sort of symmetry too - around the point of origin. If you graph this specific function (for example, on the Wolfram Alpha website), you can see that the function has none of these symmetries. To prove that the function is NOT even, nor odd, just find a number for which f(x) is neither f(-x) nor -f(-x). Actually proving that a function IS even or odd (assuming it actually is) is more complicated, of course - you have to prove that it has the "even" or the "odd" property for EVERY value of x. Let f(x) = 2x3 - x2. Notice that f is defined for any x, since it is a polynomial function. If f(-x) = f(x), then f is even. If f(-x) = -f(x), then f is odd. f(-x) = 2(-x)3 - (-x)2 = -2x3 - x2 Since f(-x) ≠ f(x) = 2x3 - x2, f is not even. Since f(-x) ≠ - f(x) = -(2x3 - x2) = -2x3 + x2, f is not odd. Therefore f is neither even nor odd.
its graph is symetric x-axises
An even number can be divided by 2 evenly. An odd number will have a remainder of 1 when divided by 2. A function can be either.