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JEE Advanced 2026 · Continuity and Differentiability

For a real number α, let [α] denote the greatest integer less than or equal to α. For a finite set S, let |S| denote the number of elements in the set S. Consider the functions f:(−3,3)→(−f : (-3,3) \to (-inf, inf) and g:(−3,3)→(−g : (-3,3) \to (-inf, inf) 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= \{x in (-3,3) : f is discontinuous at x}x\} and B={xB = \{x in (-3,3) : g is discontinuous at x}.x\}. Then the value of |A| + 2|B| - |A ∩ B| is ________.

Answer: 5656

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Written solution

For a real number α, let [α] denote the greatest integer less than or equal to α. For a finite set S, let |S| denote the number of elements in the set S. Consider the functions f: (-3, 3) → (-∞, ∞) and g: (-3, 3) → (-∞, ∞) defined by f(x) = [x³] logₑ(1 + sin²(π(x - [x]))) and g(x) = x³ sin²(π logₑ(1 + x - [x])). Let A = {x ∈ (-3, 3) : f is discontinuous at x} and B = {x ∈ (-3, 3) : g is discontinuous at x}. Then the value of |A| + 2|B| - |A ∩ B| is ________.

f(x)=[x3]log⁡e ⁣(1+sin⁡2 ⁣(π(x−[x])))f(x) = [x^{3}]\log_e\!\left(1+\sin^{2}\!\left(\pi(x-[x])\right)\right)

g(x)=x3sin⁡2 ⁣(πlog⁡e(1+x−[x]))g(x) = x^{3}\sin^{2}\!\left(\pi\log_e(1+x-[x])\right)

domain (−3,3)\text{domain } (-3,3)

A={x:f discontinuous},B={x:g discontinuous}A = \{x: f \text{ discontinuous}\},\quad B = \{x: g \text{ discontinuous}\}

Find ∣A∣+2∣B∣−∣A∩B∣\text{Find } |A| + 2|B| - |A\cap B|

1. simplify f1.\ \text{simplify } f

2. count A2.\ \text{count } A

3. count B and A∩B3.\ \text{count } B \text{ and } A\cap B

sin⁡2 ⁣(π(x−[x]))=sin⁡2(πx)\sin^{2}\!\left(\pi(x-[x])\right) = \sin^{2}(\pi x)

⇒ f(x)=[x3]log⁡ ⁣(1+sin⁡2(πx))\Rightarrow\ f(x) = [x^{3}]\log\!\left(1+\sin^{2}(\pi x)\right)

h(x)=log⁡ ⁣(1+sin⁡2(πx)) is continuoush(x) = \log\!\left(1+\sin^{2}(\pi x)\right) \text{ is continuous}

[x3] jumps where x3∈Z,x3∈(−27,27)[x^{3}] \text{ jumps where } x^{3}\in\mathbb{Z},\quad x^{3}\in(-27,27)

#{x3∈Z}=53(n=−26,−25,…,26)\#\{x^{3}\in\mathbb{Z}\} = 53\quad (n=-26,-25,\ldots,26)

jump points: x=n3\text{jump points: } x = \sqrt[3]{n}

h=0⇔x∈Z: x=−2,−1,0,1,2 (integer cubes)h=0 \Leftrightarrow x\in\mathbb{Z}:\ x = -2,-1,0,1,2\ (\text{integer cubes})

∣A∣=53−5=48|A| = 53 - 5 = 48

g(x)=x3sin⁡2 ⁣(πlog⁡(1+{x}))g(x) = x^{3}\sin^{2}\!\left(\pi\log(1+\{x\})\right)

x3 continuous⇒break only where {x} jumps (integers)x^{3} \text{ continuous} \Rightarrow \text{break only where } \{x\} \text{ jumps (integers)}

at integer n≠0: n3sin⁡2(πlog⁡2)≠g(n)=0 (jump)\text{at integer } n\neq 0:\ n^{3}\sin^{2}(\pi\log 2) \neq g(n)=0\ (\text{jump})

at 0: x3=0⇒g continuous\text{at } 0:\ x^{3}=0 \Rightarrow g \text{ continuous}

B={−2,−1,1,2}⇒∣B∣=4B = \{-2,-1,1,2\} \Rightarrow |B| = 4

A∩B=∅⇒∣A∩B∣=0A\cap B = \varnothing \Rightarrow |A\cap B| = 0

∣A∣+2∣B∣−∣A∩B∣=48+2(4)−0=56|A| + 2|B| - |A\cap B| = 48 + 2(4) - 0 = 56

56\boxed{56}

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