Concept:A rational expression is undefined wherever its denominator equals zero.Explanation:The given expression is x2+2x−35x2−9x+18.It is undefined only when the denominator is 0.So, solve x2+2x−35=0.Factorise the quadratic: x2+7x−5x−35=0.This gives (x+7)(x−5)=0.Hence, x+7=0 or x−5=0.Therefore, x=−7 or x=5.Answer:x=−7 or x=5, which matches option C.