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NDA 2026
Exam
NDA
Year
2026
Subject
Mathematics
Chapter
Continuity and Differentiability

NDA 2026 · Mathematics · Continuity and Differentiability

Passage: Let f(x)= (x^2) and g(x)=x|x| for |x| Question: If...

Passage: Let f(x)=tan⁡(x2)f(x)=\tan(x^2) and g(x)=x∣x∣g(x)=x|x| for ∣x∣<π2|x|< \sqrt{\dfrac{\pi}{2}}.

Question: If p(x)=f(x)g(x)p(x)=f(x)g(x), then which of the following statements is/are correct ?
I. p(x)p(x) is continuous at x=0x=0.
II. p(x)p(x) is differentiable at x=0x=0.
Select the answer using the code given below :

Options

  1. AI only
  2. BII only
  3. CBoth I and II
  4. DNeither I nor II

Correct answer

C. Both I and II

Step-by-step solution

Given f(x)=tan⁡(x2)f(x) = \tan(x^2) and g(x)=x∣x∣g(x) = x|x|.

The function p(x)p(x) is given by p(x)=f(x)g(x)=x∣x∣tan⁡(x2)p(x) = f(x)g(x) = x|x|\tan(x^2).

We can redefine p(x)p(x) as:
p(x)=x2tan⁡(x2)p(x) = x^2 \tan(x^2) for x≥0x \ge 0
p(x)=−x2tan⁡(x2)p(x) = -x^2 \tan(x^2) for x<0x < 0

Checking continuity at x=0x = 0:
lim⁡x→0+p(x)=lim⁡x→0+x2tan⁡(x2)=0\lim_{x \to 0^+} p(x) = \lim_{x \to 0^+} x^2 \tan(x^2) = 0
lim⁡x→0−p(x)=lim⁡x→0−−x2tan⁡(x2)=0\lim_{x \to 0^-} p(x) = \lim_{x \to 0^-} -x^2 \tan(x^2) = 0
p(0)=0p(0) = 0
Since lim⁡x→0+p(x)=lim⁡x→0−p(x)=p(0)\lim_{x \to 0^+} p(x) = \lim_{x \to 0^-} p(x) = p(0), p(x)p(x) is continuous at x=0x = 0. Statement I is correct.

Checking differentiability at x=0x = 0:
Right Hand Derivative (RHD) at x=0x = 0:
lim⁡h→0+p(h)−p(0)h=lim⁡h→0+h2tan⁡(h2)−0h=lim⁡h→0+htan⁡(h2)=0\lim_{h \to 0^+} \dfrac{p(h) - p(0)}{h} = \lim_{h \to 0^+} \dfrac{h^2 \tan(h^2) - 0}{h} = \lim_{h \to 0^+} h \tan(h^2) = 0

Left Hand Derivative (LHD) at x=0x = 0:
lim⁡h→0−p(h)−p(0)h=lim⁡h→0−−h2tan⁡(h2)−0h=lim⁡h→0−−htan⁡(h2)=0\lim_{h \to 0^-} \dfrac{p(h) - p(0)}{h} = \lim_{h \to 0^-} \dfrac{-h^2 \tan(h^2) - 0}{h} = \lim_{h \to 0^-} -h \tan(h^2) = 0

Since RHD = LHD = 00, p(x)p(x) is differentiable at x=0x = 0. Statement II is correct.

Both statements I and II are correct.

Answer: Both I and II
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