Given L=x→1limx−1x2−ax+b=5
As x→1, the denominator becomes zero, hence for finite limit, the numerator must also approach to zero as x→1
⇒1−a+b=0
⇒b=a−1…(1)
Now L=x→1limx−1x2−ax+b (00) form
By using L'Hospital Rule,
⇒L=x→1lim12x−a
⇒L=x→1lim12x−a=5
⇒2−a=5⇒a=−3
From the equation (1), we get
⇒b=a−1=−4
⇒a+b=−7.