This past week in Pre Calculus 11 we started unit 7: Rational Expressions and Equations. Something I learned this week was how to simplify an expression. If the equation was both (x+4) on the top and bottom cancel out leaving . A non-permissible value means if that number was substituted in for a variable it would make the denominator a 0 which is not what we want so it can not be these values. Looking at the original equation (x+4) and (x+6) are on the bottom so their non-permissible value would be -4 and -6.