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JEE Advanced 2026Paper 2
Exam
JEE Advanced
Year
2026
Paper
Paper 2
Subject
Mathematics
Chapter
Continuity and Differentiability

JEE Advanced 2026 · Paper 2 · Mathematics · Continuity and Differentiability

For a real number α , let [α] denote the greatest integer less than...

For a real number α\alpha, let [α][\alpha] denote the greatest integer less than or equal to α\alpha. For a finite set SS, let ∣S∣|S| denote the number of elements in the set SS.
Consider the functions f:(−3,3)→(−∞,∞)f : (-3, 3) \rightarrow (-\infty, \infty) and g:(−3,3)→(−∞,∞)g : (-3, 3) \rightarrow (-\infty, \infty) defined by
f(x)=[x3]log⁡e(1+sin⁡2(π(x−[x])))f(x) = [x^3]\log_e(1 + \sin^2(\pi(x - [x])))
and
g(x)=x3sin⁡2(πlog⁡e(1+x−[x]))g(x) = x^3 \sin^2(\pi \log_e(1 + x - [x])).
Let
A={x∈(−3,3):f is discontinuous at x}A = \{x \in (-3, 3) : f \text{ is discontinuous at } x\}
and
B={x∈(−3,3):g is discontinuous at x}B = \{x \in (-3, 3) : g \text{ is discontinuous at } x\}.
Then the value of ∣A∣+2∣B∣−∣A∩B∣|A| + 2|B| - |A \cap B| is ___________.

Correct answer

0

Step-by-step solution

For the function f(x)=[x3]log⁡e(1+sin⁡2(π(x−[x])))f(x) = [x^3]\log_e(1 + \sin^2(\pi(x - [x]))), we can simplify the argument of the sine function. Since [x][x] is an integer, sin⁡(π(x−[x]))=sin⁡(πx−π[x])=±sin⁡(πx)\sin(\pi(x - [x])) = \sin(\pi x - \pi[x]) = \pm \sin(\pi x). Thus, sin⁡2(π(x−[x]))=sin⁡2(πx)\sin^2(\pi(x - [x])) = \sin^2(\pi x).

The function f(x)f(x) can be rewritten as f(x)=[x3]log⁡e(1+sin⁡2(πx))f(x) = [x^3]\log_e(1 + \sin^2(\pi x)).
The term log⁡e(1+sin⁡2(πx))\log_e(1 + \sin^2(\pi x)) is continuous everywhere. The term [x3][x^3] has jump discontinuities where x3x^3 is an integer. For x∈(−3,3)x \in (-3, 3), x3∈(−27,27)x^3 \in (-27, 27). The integer values of x3x^3 in this interval are k∈{−26,−25,…,26}k \in \{-26, -25, \dots, 26\}, which gives 5353 points of the form x=k1/3x = k^{1/3}.

At these points, [x3][x^3] is discontinuous. For f(x)f(x) to be continuous at x=k1/3x = k^{1/3}, the continuous factor must be zero:
log⁡e(1+sin⁡2(πx))=0  ⟹  sin⁡2(πx)=0  ⟹  x\log_e(1 + \sin^2(\pi x)) = 0 \implies \sin^2(\pi x) = 0 \implies x is an integer.
The integers in (−3,3)(-3, 3) are −2,−1,0,1,2-2, -1, 0, 1, 2. Their cubes are −8,−1,0,1,8-8, -1, 0, 1, 8, which are 55 values among the 5353 points. At these 55 points, f(x)f(x) is continuous. At the remaining 53−5=4853 - 5 = 48 points, f(x)f(x) is discontinuous.
Thus, ∣A∣=48|A| = 48.

For the function g(x)=x3sin⁡2(πlog⁡e(1+x−[x]))g(x) = x^3 \sin^2(\pi \log_e(1 + x - [x])), we can write x−[x]={x}x - [x] = \{x\}, which is the fractional part of xx.
The function g(x)=x3sin⁡2(πlog⁡e(1+{x}))g(x) = x^3 \sin^2(\pi \log_e(1 + \{x\})) is continuous everywhere except possibly at the integers, where {x}\{x\} is discontinuous.
The integers in (−3,3)(-3, 3) are c∈{−2,−1,0,1,2}c \in \{-2, -1, 0, 1, 2\}.
Let's check the continuity at x=cx = c:
Right-hand limit (x→c+x \to c^+): {x}→0\{x\} \to 0, so g(x)→c3sin⁡2(πlog⁡e1)=0g(x) \to c^3 \sin^2(\pi \log_e 1) = 0.
Left-hand limit (x→c−x \to c^-): {x}→1\{x\} \to 1, so g(x)→c3sin⁡2(πlog⁡e2)g(x) \to c^3 \sin^2(\pi \log_e 2).

For g(x)g(x) to be continuous at x=cx = c, we must have c3sin⁡2(πlog⁡e2)=0c^3 \sin^2(\pi \log_e 2) = 0. Since log⁡e2≈0.693\log_e 2 \approx 0.693, πlog⁡e2\pi \log_e 2 is not an integer multiple of π\pi, meaning sin⁡2(πlog⁡e2)≠0\sin^2(\pi \log_e 2) \neq 0. Therefore, we must have c3=0  ⟹  c=0c^3 = 0 \implies c = 0.
So, g(x)g(x) is continuous at x=0x = 0 and discontinuous at x∈{−2,−1,1,2}x \in \{-2, -1, 1, 2\}.
Thus, B={−2,−1,1,2}B = \{-2, -1, 1, 2\} and ∣B∣=4|B| = 4.

Since AA contains no integers and BB contains only integers, A∩B=∅A \cap B = \emptyset, which means ∣A∩B∣=0|A \cap B| = 0.

Finally, we calculate the required value:
∣A∣+2∣B∣−∣A∩B∣=48+2(4)−0=48+8=56|A| + 2|B| - |A \cap B| = 48 + 2(4) - 0 = 48 + 8 = 56.

Answer: 5656
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