Continuity and Differentiability · Class 12 · CBSE · Science Mathematics

Define f(x) = (1 − cos x)/x² for x ≠ 0 and f(0) = 1/2. What can be concluded about f at x = 0?

Practice question from Continuity and Differentiability (Class 12 · CBSE · Science Mathematics), with the correct answer and a step-by-step solution.

medium · MCQ · Q-9075FA

Define f(x) = (1 − cos x)/x² for x ≠ 0 and f(0) = 1/2. What can be concluded about f at x = 0?

  1. A.f is both continuous and differentiable at x = 0Correct answer
  2. B.f is continuous but not differentiable at x = 0
  3. C.f is differentiable but not continuous at x = 0
  4. D.f is neither continuous nor differentiable at x = 0

Solution

Using lim⁡x→01−cos⁡xx2=12\lim_{x\to 0}\frac{1-\cos x}{x^2}=\frac{1}{2}, f is continuous at 0. Also, f(h)−f(0)h→0\frac{f(h)-f(0)}{h}\to 0 as h→0h\to 0, so f is differentiable at 0.

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