Editing Comparative statics (section)

===Many equations and unknowns===
All the equations above remain true in the case of a system of <math>n</math> equations in <math>n</math> unknowns.  In other words, suppose <math>f(x,a)=0</math> represents a system of <math>n</math> equations involving the vector of <math>n</math> unknowns <math>x</math>, and the vector of <math>m</math> given parameters <math>a</math>.  If we make a sufficiently small change <math>\text{d}a</math> in the parameters, then the resulting changes in the endogenous variables can be approximated arbitrarily well by <math>\text{d}x = -B^{-1}C \text{d}a</math>.  In this case, <math>B</math> represents the <math>n</math>×<math>n</math> [[Jacobian matrix|matrix of partial derivatives]] of the functions <math>f</math> with respect to the variables <math>x</math>, and <math>C</math> represents the <math>n</math>×<math>m</math> matrix of partial derivatives of the functions <math>f</math> with respect to the parameters <math>a</math>. (The derivatives in <math>B</math> and <math>C</math> are evaluated at the initial values of <math>x</math> and <math>a</math>.) Note that if one wants just the comparative static effect of one exogenous variable on one endogenous variable, [[Cramer's Rule]] can be used on the [[Total differentiation#The total derivative via differentials|totally differentiated]] system of equations <math>B\text{d}x + C \text{d}a \,=0</math>.