Class CBSE Class 12 Mathematics Continuity and Differentiability Q #1691
COMPETENCY BASED
APPLY
1 Marks 2026 AISSCE(Board Exam) MCQ SINGLE
If $f(x)=\begin{cases}\frac{x^{2}-4x-5}{x+1},&x\ne-1\\k,&x=-1\end{cases}$ is continuous at $x=-1$ then the value of k is:
(A) Any real value
(B) 6
(C) -1
(D) -6
Correct Answer: D

AI Tutor Explanation

Powered by Gemini

Detailed Solution

Step 1: Understand the condition for continuity

A function $f(x)$ is continuous at $x = a$ if the limit of the function as $x$ approaches $a$ exists and is equal to the value of the function at $a$. Mathematically, $\lim_{x \to -1} f(x) = f(-1)$.

Step 2: Evaluate the limit

We need to find $\lim_{x \to -1} \frac{x^{2}-4x-5}{x+1}$. Substituting $x = -1$ directly gives the indeterminate form $\frac{0}{0}$. We factorize the numerator:

$$x^{2}-4x-5 = (x-5)(x+1)$$

Now, substitute this back into the limit:

$$\lim_{x \to -1} \frac{(x-5)(x+1)}{x+1} = \lim_{x \to -1} (x-5)$$

Step 3: Solve for k

Evaluating the limit as $x \to -1$: $$-1 - 5 = -6$$ Since the function is continuous at $x = -1$, we must have $f(-1) = \lim_{x \to -1} f(x)$. Given $f(-1) = k$, we conclude $k = -6$.

Final Answer: -6

AI Suggestion: Option D

AI generated content. Review strictly for academic accuracy.

Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student must apply the definition of continuity and algebraic limit techniques to solve for an unknown constant.
Knowledge Dimension: PROCEDURAL
Justification: The problem requires a step-by-step algorithmic approach involving factorization and limit evaluation.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. It tests the fundamental understanding of continuity in the chapter 'Continuity and Differentiability'.