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In mathematics, a constant function is a function whose (output) value is the same for every input value. For example, the function is a constant function because the value of is 4 regardless of the input value (see image). ==Basic properties== As a real-valued function of a real-valued argument, a constant function has the general form or just . :Example: The function or just is the specific constant function where the output value is . The domain of this function is the set of all real numbers ℝ. The codomain of this function is just . The independent variable ''x'' does not appear on the right side of the function expression and so its value is "vacuously substituted". Namely ''y''(0)=2, ''y''(−2.7)=2, ''y''(π)=2,.... No matter what value of ''x'' is input, the output is "2". :Real-world example: A store where every item is sold for the price of 1 euro. The graph of the constant function is a horizontal line in the plane that passes through the point . In the context of a polynomial in one variable ''x'', the non-zero constant function is a polynomial of degree 0 and its general form is . This function has no intersection point with the ''x''-axis, that is, it has no root (zero). On the other hand, the polynomial is the identically zero function. It is the (trivial) constant function and every ''x'' is a root. Its graph is the ''x''-axis in the plane. A constant function is an even function, i.e. the graph of a constant function is symmetric with respect to the ''y''-axis. In the context where it is defined, the derivative of a function is a measure of the rate of change of function values with respect to change in input values. Because a constant function does not change, its derivative is 0. This is often written: . The converse is also true. Namely, if ''y'''(''x'')=0 for all real numbers ''x'', then ''y''(''x'') is a constant function.〔(【引用サイトリンク】title=Zero Derivative implies Constant Function )〕 :Example: Given the constant function . The derivative of ''y'' is the identically zero function . 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Constant function」の詳細全文を読む スポンサード リンク
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