In mathematics, a coefficient is a constant multiplicative factor of a certain object. The object can be such things as a variable, a vector, a function, etc. For example, the coefficient of 9x2 is 9. In some cases, the objects and the coefficients are indexed in the same way, leading to expressions such as
圖片參考：http://upload.wikimedia.org/math/7/6/b/76bbf332239e3492d6b1e486daa370c1.png
where an is the coefficient of the variable xn for each n = 1, 2, 3, …
第一位給出的例子是錯的