Concept:For a finite non-zero limit, both numerator and denominator must become zero at
x=1, and their orders of zeroes must match.
Explanation:At
x=1, the numerator becomes
sin(0)−1+1=0.
Since the given limit is
−2, a non-zero finite value, the denominator must also become
0 at
x=1.
So,
2(1)3−7(1)2+a(1)+b=0, which gives
a+b=5.
Near
x=1, we have
3x2−4x+1=(x−1)(3x−1)→0.
Using
siny∼y for small
y, the numerator behaves like
(3x2−4x+1)−x2+1=2x2−4x+2=2(x−1)2.
Thus, the numerator has factor
(x−1)2.
For a non-zero limit, the denominator must also have factor
(x−1)2.
So, the derivative of the denominator must vanish at
x=1.
The derivative is
6x2−14x+a.
At
x=1,
6−14+a=0, giving
a=8.
Using
a+b=5, we get
b=−3.
The quadratic equation with roots
8 and
−3 is
x2−(8+(−3))x+8(−3)=0, i.e.
x2−5x−24=0.
Answer:x2−5x−24=0Hence, the correct option is C.