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JEE Advanced 2026Paper 1
Exam
JEE Advanced
Year
2026
Paper
Paper 1
Subject
Mathematics
Chapter
Continuity and Differentiability

JEE Advanced 2026 · Paper 1 · Mathematics · Continuity and Differentiability

Consider the function f : (-(π)/(2), (π)/(2)) arrow (-∞, ∞) defined...

Consider the function f:(−π2,π2)→(−∞,∞)f : \left(-\dfrac{\pi}{2}, \dfrac{\pi}{2}\right) \rightarrow (-\infty, \infty) defined by

f(x)=(∣x∣+∣x−1∣)sin⁡x+[xsin⁡x]f(x) = (|x| + |x - 1|) \sin x + [x \sin x],

where [xsin⁡x][x \sin x] is the greatest integer less than or equal to xsin⁡xx \sin x.

Let α\alpha be the total number of points in the interval \left(-\dfrac{\pi}{2}, \dfrac{\pi}{2}\right)atwhichat whichfisNOTcontinuous,andletis NOT continuous, and let\betabethetotalnumberofpointsintheinterval(−π2,π2)be the total number of points in the interval \left(-\dfrac{\pi}{2}, \dfrac{\pi}{2}\right) at which ff is NOT differentiable.

Then the value of α+β\alpha + \beta is ___________.

Correct answer

0

Step-by-step solution

Let f(x)=g(x)+h(x)f(x) = g(x) + h(x), where g(x)=(∣x∣+∣x−1∣)sin⁡xg(x) = (|x| + |x - 1|) \sin x and h(x)=[xsin⁡x]h(x) = [x \sin x].

First, we analyze h(x)=[xsin⁡x]h(x) = [x \sin x] on the interval \left(-\dfrac{\pi}{2}, \dfrac{\pi}{2}\right).<br>Thefunction.<br>The functiony = x \sin xisanevenfunction.Foris an even function. Forx \in \left[0, \dfrac{\pi}{2}\right),,x \sin xisstrictlyincreasing.<br>Atis strictly increasing. <br>Atx = 0,,x \sin x = 0.<br>As.<br>Asx \to \dfrac{\pi}{2},,x \sin x \to \dfrac{\pi}{2} \approx 1.57.<br>Thus,.<br>Thus,x \sin x \in [0, 1.57)forforx \in \left(-\dfrac{\pi}{2}, \dfrac{\pi}{2}\right).<br>Thevalueof.<br>The value of[x \sin x]willbewill be0whenwhen0 \le x \sin x < 1,and, and1whenwhen1 \le x \sin x < \dfrac{\pi}{2}.<br>Let.<br>Letx_1 \in \left(0, \dfrac{\pi}{2}\right)betheuniquepointwherebe the unique point wherex_1 \sin x_1 = 1.Bysymmetry,. By symmetry,-x_1istheuniquepointin(−π2,0)is the unique point in \left(-\dfrac{\pi}{2}, 0\right) where (−x1)sin⁡(−x1)=1(-x_1) \sin(-x_1) = 1.
Therefore, h(x)h(x) has jump discontinuities at exactly two points: x=x1x = x_1 and x=−x1x = -x_1.
At x=0x = 0, xsin⁡x=0x \sin x = 0 and is non-negative in its neighborhood, so [xsin⁡x]=0[x \sin x] = 0 around x=0x = 0, making h(x)h(x) continuous and differentiable at x=0x = 0.

Next, we analyze g(x)=(∣x∣+∣x−1∣)sin⁡xg(x) = (|x| + |x - 1|) \sin x.
The absolute value functions have critical points at x=0x = 0 and x=1x = 1.
For xx in a small neighborhood of 00 (specifically x∈(−1,1)x \in (-1, 1)):
If x∈[0,1)x \in [0, 1), g(x)=(x−(x−1))sin⁡x=sin⁡x⇒g′(0+)=cos⁡0=1g(x) = (x - (x - 1)) \sin x = \sin x \Rightarrow g'(0^+) = \cos 0 = 1.
If x∈(−1,0)x \in (-1, 0), g(x)=(−x−(x−1))sin⁡x=(1−2x)sin⁡x⇒g′(0−)=−2sin⁡0+1⋅cos⁡0=1g(x) = (-x - (x - 1)) \sin x = (1 - 2x) \sin x \Rightarrow g'(0^-) = -2 \sin 0 + 1 \cdot \cos 0 = 1.
Since g′(0+)=g′(0−)g'(0^+) = g'(0^-), g(x)g(x) is differentiable at x=0x = 0.

For xx in a small neighborhood of 11:
If x∈(0,1]x \in (0, 1], g(x)=sin⁡x⇒g′(1−)=cos⁡1g(x) = \sin x \Rightarrow g'(1^-) = \cos 1.
If x∈(1,π2)x \in \left(1, \dfrac{\pi}{2}\right), g(x)=(x+(x−1))sin⁡x=(2x−1)sin⁡x⇒g′(1+)=2sin⁡1+1⋅cos⁡1g(x) = (x + (x - 1)) \sin x = (2x - 1) \sin x \Rightarrow g'(1^+) = 2 \sin 1 + 1 \cdot \cos 1.
Since g′(1−)≠g′(1+)g'(1^-) \neq g'(1^+), g(x)g(x) is not differentiable at x=1x = 1.

Now, combining the results for f(x)=g(x)+h(x)f(x) = g(x) + h(x):
1. Discontinuities: g(x)g(x) is continuous everywhere. h(x)h(x) is discontinuous at x1x_1 and −x1-x_1. Thus, f(x)f(x) is discontinuous at 22 points. ⇒α=2\Rightarrow \alpha = 2.
2. Non-differentiability: f(x)f(x) is not differentiable where it is discontinuous (x1x_1 and −x1-x_1). Additionally, at x=1x = 1, h(x)h(x) is constant (00) because 1⋅sin⁡1≈0.84<11 \cdot \sin 1 \approx 0.84 < 1, meaning h(x)h(x) is differentiable at x=1x = 1. However, g(x)g(x) is not differentiable at x=1x = 1. Thus, f(x)f(x) is not differentiable at x=1x = 1.
This gives 33 points of non-differentiability: −x1,1,x1-x_1, 1, x_1. ⇒β=3\Rightarrow \beta = 3.

Finally, α+β=2+3=5\alpha + \beta = 2 + 3 = 5.

Answer: 55
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