Question 187081
Remember, division by zero is NOT defined. So this means that ANY values that make the denominator of {{{(b-5)/(5b-20)}}} equal to zero will also make the expression undefined.



{{{(b-5)/(5b-20)}}} Start with the given expression.



{{{5b-20=0}}} Set the denominator equal to zero.



{{{5b=0+20}}} Add {{{20}}} to both sides.



{{{5b=20}}} Combine like terms on the right side.



{{{b=(20)/(5)}}} Divide both sides by {{{5}}} to isolate {{{b}}}.



{{{b=4}}} Reduce.



So when {{{b=4}}}, the expression {{{5b-20}}} is equal to zero.



In turn, when {{{b=4}}} the denominator of {{{(b-5)/(5b-20)}}} is equal to zero.



So if {{{b=4}}} this makes the expression {{{(b-5)/(5b-20)}}} undefined.