Coefficient

In mathematics, a coefficient is a multiplicative factor in some term of a polynomial, a series, or any expression; it is usually a number, but may be any expression (including variables such as , and ). When variables appear in the coefficients, they are often called parameters, and must be clearly distinguished from those representing other variables in an expression. 
For example, 
formula_1, has the real coefficients 2, -1, and 3 respectively, and 
formula_2, has coefficient parameters a, b, and c respectively assuming x is the variable of the equation. 
The constant coefficient is the coefficient not attached to variables in an expression. For example, the constant coefficients of the expressions above are the real coefficient 3 and the parameter represented by "c". 
Similarly, the coefficient attached to the highest multiplicity of the variable in a polynomial is referred to as the leading coefficient. For example in the expressions above, the leading coefficients are 2 and the parameter represented by "a".
The binomial coefficients occur in the expanded form of formula_3, and are tabulated in Pascal's triangle.
Terminology and Definition.
In mathematics, a coefficient is a multiplicative factor in some term of a polynomial, a series, or any expression;
For example, in
the first two terms have the coefficients 7 and −3, respectively. The third term 1.5 is a constant coefficient. The final term does not have any explicitly-written coefficient factor that would not change the term; the coefficient is thus taken to be 1 (since variables without number have a coefficient of 1).
In many scenarios, coefficients are numbers (as is the case for each term of the above example), although they could be parameters of the problem—or any expression in these parameters. In such a case, one must clearly distinguish between symbols representing variables and symbols representing parameters. Following René Descartes, the variables are often denoted by , , ..., and the parameters by , , , ..., but this is not always the case. For example, if is considered a parameter in the above expression, then the coefficient of would be , and the constant coefficient (always with respect to ) would be .
When one writes 
it is generally assumed that is the only variable, and that , and are parameters; thus the constant coefficient is in this case.
Similarly, any polynomial in one variable can be written as
for some positive integer formula_7, where formula_8 are coefficients; to allow this kind of expression in all cases, one must allow introducing terms with 0 as coefficient.
For the largest formula_9 with formula_10 (if any), formula_11 is called the leading coefficient of the polynomial. For example, the leading coefficient of the polynomial
is 4.
Some specific coefficients that occur frequently in mathematics have dedicated names. For example, the binomial coefficients occur in the expanded form of formula_3, and are tabulated in Pascal's triangle.
Linear algebra.
In linear algebra, a system of linear equations is associated with a coefficient matrix, which is used in Cramer's rule to find a solution to the system.
The leading entry (sometimes "leading coefficient") of a row in a matrix is the first nonzero entry in that row. So, for example, given the matrix described as follows:
the leading coefficient of the first row is 1; that of the second row is 2; that of the third row is 4, while the last row does not have a leading coefficient.
Though coefficients are frequently viewed as constants in elementary algebra, they can also be viewed as variables as the context broadens. For example, the coordinates formula_15 of a vector formula_16 in a vector space with basis formula_17, are the coefficients of the basis vectors in the expression 