I don't understand their reasoning when they say "this equation is false if and only if 1-7p=0". Why? Is it because you can't divide by 0? But if that were the case, then it wouldn't be false, it would be impossible.
#Question
patent ridge
novel elkBOT
gaunt cradle
When you have an expression of the form $a/b$, the latter is only defined when $b\neq 0$, otherwise, i.e., when $b=0$, the expression $a/b=a/0$ is undefined.
violet jewelBOT
bondalton
gaunt cradle
Therefore, in the example, we have that $x=\frac{-28}{1-7p}$ is '\emph{legit}' if and only if $1-7p\neq 0$.
dire thunder
When the x combine to 0 then its impossible for them to equal something other than 0