Question 881196
I'm assuming the rational expression is {{{(x+3)/(x^2+3x-28)}}}



The rational expression is undefined when the denominator is zero.



To find the values that make it undefined, set the denominator equal to zero and solve



x^2+3x-28 = 0



(x+7)(x-4) = 0



x+7 = 0 or x-4 = 0



x = -7 or x = 4



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The rational expression is undefined when <font color="red">x = -7 or x = 4</font> since these values cause the denominator to be zero leading to a division by zero error.