SOLUTION: which real numbers cannot be used in place of the variable in the rational expression? (3b+1)/(b^2-3b-4)

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Question 939889: which real numbers cannot be used in place of the variable in the rational expression?
(3b+1)/(b^2-3b-4)
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

%283b%2B1%29%2F%28b%5E2-3b-4%29 to have a real solution, denominator cannot be equal to zero; so, find the value(s) of b that makes denominator equal to zero
b%5E2-3b-4=0 ...factor completely
b%5E2%2Bb-4b-4=0 ...group
%28b%5E2%2Bb%29-%284b%2B4%29=0
b%28b%2B1%29-4%28b%2B1%29=0
%28b-4%29%28b%2B1%29=0
solutions:
if %28b-4%29=0 => b=4
if %28b%2B1%29=0 => b=-1

real numbers b=4 and b=-1 cannot be used in place of the variable in the rational expression