REworking links of review

http://www.purplemath.com/modules/fcns.htm

http://www.virtualnerd.com/algebra-1/linear-equation-analysis/slope-rate-of-change/understanding-slope/slope-formula-definition

http://www.virtualnerd.com/pre-algebra/polynomials-nonlinear-functions/non-linear/linear/table-linear-vs-nonlinear

http://www.virtualnerd.com/pre-algebra/linear-functions-graphing/rate-of-change-slope/rate-of-change/rate-of-change-two-points-table

http://www.virtualnerd.com/algebra-1/linear-equation-analysis/slope-intercept-form-definition.php

http://www.khanacademy.org/math/cc-eighth-grade-math/cc-8th-relationships-functions/linear-nonlinear-functions-tut/v/linear-and-nonlinear-functions-example-2