Class CBSE Class 12 Mathematics Continuity and Differentiability Q #1252
KNOWLEDGE BASED
REMEMBER
3 Marks 2024 AISSCE(Board Exam) SA
Find the value of a and b so that function f defined as : $$ f(x) = \begin{cases} \frac{x-2}{|x-2|} + a, & \text{if } x < 2 \\ a+b, & \text{if } x = 2 \\ \frac{x-2}{|x-2|} + b, & \text{if } x > 2 \end{cases} $$ is a continuous function.

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Detailed Solution

Step 1: Understanding Continuity

For the function $f(x)$ to be continuous at $x=2$, the left-hand limit (LHL) and the right-hand limit (RHL) at $x=2$ must be equal, and also equal to the value of the function at $x=2$.

Step 2: Calculate the Left-Hand Limit (LHL)

The left-hand limit is given by: $$LHL = \lim_{x \to 2^-} f(x) = \lim_{x \to 2^-} \frac{x-2}{x-2} = 1$$

Step 3: Calculate the Right-Hand Limit (RHL)

The right-hand limit is given by: $$RHL = \lim_{x \to 2^+} f(x) = \lim_{x \to 2^+} (ax^2 - bx + 3)$$ Since the function is a polynomial for $x > 2$, we can directly substitute $x=2$: $$RHL = a(2)^2 - b(2) + 3 = 4a - 2b + 3$$

Step 4: Evaluate the function at x=2

The value of the function at $x=2$ is given as $f(2) = 1 + a$.

Step 5: Apply the Continuity Condition

For continuity, we must have $LHL = RHL = f(2)$. Therefore, we have two equations: 1. $1 = 4a - 2b + 3$ 2. $1 = 1 + a$

Step 6: Solve the Equations

From equation (2), we get: $1 = 1 + a \implies a = 0$ Substitute $a = 0$ into equation (1): $1 = 4(0) - 2b + 3 \implies 1 = -2b + 3 \implies 2b = 2 \implies b = 1$

Step 7: Final Answer

Therefore, $a = 0$ and $b = 1$.

Final Answer: a = 0, b = 1

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Pedagogical Audit
Bloom's Analysis: This is an REMEMBER question because it requires recalling the definition of continuity and applying it to solve for the unknown variables.
Knowledge Dimension: CONCEPTUAL
Justification: The question tests the understanding of the concept of continuity of a function at a point and how to apply the conditions for continuity to find unknown parameters.
Syllabus Audit: In the context of CBSE Class 12, this is classified as KNOWLEDGE. It directly relates to the textbook definition and application of continuity of functions.