Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
JEE Main 202122 JulyMorning Shift
Exam
JEE Main
Year
2021
Date
22 July
Shift
Morning Shift
Subject
Mathematics
Chapter
Continuity and Differentiability

JEE Main 2021 · 22 July · Morning Shift · Mathematics · Continuity and Differentiability

Let f: R → R be a function defined as f(x) = \ cases 3(1 - (| x...

Let f:R→Rf: R \to R be a function defined as f\left(x\right) = \left\{\begin{cases}3\left(1 - \dfrac{| x |}{2}\right) & \text{if} & | x | \le 2 \\ 0 & \text{if} & | x | > 2\end{cases}\right .

Let g:R→Rg: R \to R be given by g(x)=f(x+2)−f(x−2).g ( x ) = f ( x + 2 ) - f ( x - 2 ) . If nn and mm denote the number of points in RR where gg is not continuous and not differentiable, respectively, then n+mn + m is equal to ________.

Let f: R → R be a function defined as f(x) = \ cases 3(1 - (| x |)/(2)) & if & | x | ≤ 2 0 & if & | x | > 2 cases . Let

Correct answer

0

Step-by-step solution

The given function is f\left(x\right) = \left\{\begin{cases}3\left(1 - \dfrac{| x |}{2}\right) & if & | x | \le 2 \\ 0 & if & | x | > 2\end{cases}\right)</p><p>By using the definition of modulus function, we have\left|x\right| = \left\{{x,x≥0−x,x<0\begin{cases}x, & x \ge 0 \\ - x, & x < 0\end{cases}\right) and also, we know that if ∣x∣≤a,⇒−a≤x≤aandif\left|x\right| \le a, ⇒ - a \le x \le a and if\left|x\right| > a, ⇒ x a,</p><p></p><p>⇒ f\left(x\right) = \left\{{3(1+x2),−2≤x≤03(1−x2),0xorx>2\begin{cases}3\left(1 + \dfrac{x}{2}\right), & - 2 \le x \le 0 \\ 3\left(1 - \dfrac{x}{2}\right), & 0 xorx > 2\end{cases}\right)

Now, f\left(x - 2\right) = \left\{\begin{cases}3\left(1 + \dfrac{x - 2}{2}\right), & - 2 \le x - 2 \le 0 \\ 3\left(1 - \dfrac{x - 2}{2}\right), & 0 x - 2orx - 2 > 2\end{cases}\right)</p><p>⇒ f\left(x - 2\right) = \left\{{3x2,0≤x≤26−3x2,2xorx>4\begin{cases}\dfrac{3x}{2}, & 0 \le x \le 2 \\ 6 - \dfrac{3x}{2}, & 2 xorx > 4\end{cases}\right)

And, f\left(x + 2\right) = \left\{\begin{cases}3\left(1 + \dfrac{x + 2}{2}\right), & - 2 \le x + 2 \le 0 \\ 3\left(1 - \dfrac{x + 2}{2}\right), & 0 x + 2orx + 2 > 2\end{cases}\right)</p><p>⇒ f\left(x + 2\right) = \left\{{6+3x2,−4≤x≤−2−3x2,−2xorx>0\begin{cases}6 + \dfrac{3x}{2}, & - 4 \le x \le - 2 \\ - \dfrac{3x}{2}, & - 2 xorx > 0\end{cases}\right)

Hence, g\left(x\right) = f\left(x + 2\right) - f\left(x - 2\right) = \left\{3x2+6,−4≤x≤−2−3x2,−2<x<23x2−6,2≤x≤40,x∈(−∞,−4)∪(4,∞)\begin{array}{ll}\dfrac{3x}{2} + 6, - 4 \le x \le - 2 \\ - \dfrac{3x}{2}, - 2 < x < 2 \\ \dfrac{3x}{2} - 6, 2 \le x \le 4 \\ 0, x \in ( - \infty , - 4 ) \cup ( 4, \infty )\end{array}\right)</p><p>The graph ofg(x)\left(x\right) is given below

Let f: R → R be a function defined as f(x) = \ cases 3(1 - (| x |)/(2)) & if & | x | ≤ 2 0 & if & | x | > 2 cases . Let

From the graph we can observe that the function gg\left(x\right)iscontinuouseverywhere,hencethenumberofpointswhereis continuous everywhere, hence the number of points whereg(x)\left(x\right) is not continuos is n=0n = 0 and the graph has sharp corners at the points \left(- 4, 0\right), \left(4, 0\right), \left(- 2, 3\right) \text{ and } \left(2, - 3\right)thusthenumberofpointswherethus the number of points whereg(x)\left(x\right) is not differentiable are m=4m = 4

⇒n+m=4.⇒ n + m = 4 .

Practice Continuity and Differentiability on Quantrex Academy →

More from Continuity and Differentiability

Let ℝ denote the set of all real numbers. Let f : ℝ arrow ℝ be an arbitrary function and… JEE Advanced 2026Consider the function f : (-(π)/(2), (π)/(2)) arrow (-∞, ∞) defined by f(x) = (|x| + |x… JEE Advanced 2026For a real number α , let [α] denote the greatest integer less than or equal to α . For a… JEE Advanced 2026For the function f(x) = e^ |x| - |x| , x ∈ ℝ , consider the following statements… JEE Main 2026Let f(x) = cases (1)/(3), & x ≤ π/2 (b(1- x))/((π-2x)^2), & x > π/2 cases . If f is… JEE Main 2026Let f(x) = cases x^3 + 8 ; & x Then the number of points, where the function g ∘ f is… JEE Main 2026Let f(x)= cases e^ x-1 , & x<0 x^2-5x+6, & x ≥ 0 cases and g(x)=f(|x|)+|f(x)| . If the… JEE Main 2026The number of points, at which the function f(x) = \ 6x, 2 + 3x^2\ + |x - 1|| |x^2… JEE Main 2026The number of points in the interval [2, 4] , at which the function f(x) = [x^2 - x… JEE Main 2026Let f(x)= _ θ arrow 0 ( π x-x^ ((2)/(θ)) (x-1) 1+x^ ((2)/(θ)) (x-1) ), x ∈ R . Consider… JEE Main 2026Let [t] denote the greatest integer less than or equal to t . If the function f(x)=\… JEE Main 2026If the function f(x)= e^ x (e^ x-x -1)+ _ e ( x+ x)-x x-x is continuous at x=0 , then the… JEE Main 2026Let α, β ∈ ℝ be such that the function f(x)= cases 2 α(x^ 2 -2)+2 β x &, x be… JEE Main 2026If f(x)=\ array cc a|x|+x^ 2 -2( |x|)( |x|) x &, x ≠ 0 b &, x=0 array . is continuous at… JEE Main 2026Let f(x)= cases a x^ 2 +2 a x+3 4 x^ 2 +4 x-3 &, x ≠-(3)/(2), (1)/(2) ~b &, x=-(3)/(2)… JEE Main 2026Let [·] denote the greatest integer function, and let f(x)= \ 2 x, x^ 2 \ . Let S = \ x… JEE Main 2026 Full Continuity and Differentiability list Continuity and Differentiability JEE Maths PYQsJEE Mathematics PYQs All JEE Main PYQs