CBSE Class 12 Mathematics Continuity and Differentiability Q #1748
COMPETENCY BASED
APPLY
2 Marks 2026 AISSCE(Board Exam) VSA
Show that the function $f(x)=\begin{cases}\frac{\cos x}{-x+\frac{\pi}{2}}, & x\ne\frac{\pi}{2} \\ 1, & x=\frac{\pi}{2}\end{cases}$ is continuous at $x=\frac{\pi}{2}$.

AI Tutor Explanation

Powered by Gemini

Detailed Solution

Step 1: Define the condition for continuity

A function $f(x)$ is continuous at $x=a$ if the limit of the function as $x$ approaches $a$ is equal to the value of the function at $a$. That is, $\lim_{x \to a} f(x) = f(a)$. Here, $a = \frac{\pi}{2}$ and $f(\frac{\pi}{2}) = 1$.

Step 2: Evaluate the limit

We need to calculate $\lim_{x \to \frac{\pi}{2}} \frac{\cos x}{-x + \frac{\pi}{2}}$. Let $h = x - \frac{\pi}{2}$. As $x \to \frac{\pi}{2}$, $h \to 0$. Then $x = h + \frac{\pi}{2}$.

Step 3: Substitute and simplify

Substituting the variables, the limit becomes: $$ \lim_{h \to 0} \frac{\cos(h + \frac{\pi}{2})}{- (h + \frac{\pi}{2}) + \frac{\pi}{2}} $$ Using the identity $\cos(\frac{\pi}{2} + h) = -\sin h$, we get: $$ \lim_{h \to 0} \frac{-\sin h}{-h} = \lim_{h \to 0} \frac{\sin h}{h} $$

Step 4: Apply standard limit result

We know that $\lim_{h \to 0} \frac{\sin h}{h} = 1$. Since the limit equals the function value $f(\frac{\pi}{2}) = 1$, the function is continuous at $x = \frac{\pi}{2}$.

Final Answer: The function is continuous as the limit equals 1.

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 trigonometric limit theorems to a specific piecewise function.
Knowledge Dimension: PROCEDURAL
Justification: The student follows a specific sequence of steps (substitution, trigonometric identity application, and limit evaluation) to reach the solution.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. This question tests the student's ability to handle indeterminate forms and piecewise continuity, which is a core competency in the Calculus unit.