... want to employ substitution, so we should ask: which variable is easier to solve for?. In this case, X (in the top equation) is easiest to solve for so we do that to obtain: Substituting into ... purposes of this tutorial that you wish to find a solution to the equation: In order to set up the problem in Goalseek, it is necessary to define a cell for the variable you want to change (X) ... Multivariable Newton Method NOTE: You may want to skip this section if you don't know how to invert matrices, add them, or multiply them. There is a multivariate extension to Newton's...