COMEDK · Maths · 25. Continuity and Differentiability

Which one of the following is not true always?

A If a function \(f(x)\) is continuous at \(x=a\), then \(\lim _{x \rightarrow a} f(x)\) exists.
B If \(f(x)\) and \(g(x)\) are differentiable at \(x=a\), then \(f(x)+g(x)\) is also differentiable at \(x=a\).
C If \(f(x)\) is continuous at \(x=a\), then it is differentiable at \(x=a\).
D If \(f(x)\) is not continuous at \(x=a\), then it is not differentiable at \(x=a\).

Verified Solution

Answer & Solution

Correct Answer

(C) If \(f(x)\) is continuous at \(x=a\), then it is differentiable at \(x=a\).

Step-by-step Solution

Detailed explanation

If a function \(f(x\) is continuous at \(x=a)\). Then, it may or may not be differentiable at \(x=a\).

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

Same subject

\(X = x_i\)	2	3	4	5
\(P(X = x_i)\)	\(\dfrac{5}{k}\)	\(\dfrac{7}{k}\)	\(\dfrac{9}{k}\)	\(\dfrac{11}{k}\)

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