Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
NTA Abhyas 2020
Exam
NTA Abhyas
Year
2020
Subject
Mathematics
Chapter
Continuity and Differentiability

NTA Abhyas 2020 · Mathematics · Continuity and Differentiability

Let f (x) = \ cases (1)/(x2) & : |x| ≥ 1 ^ 2 + β& : |x| < 1 cases...

Let ff\left(x\right) = \left\{{1x2:∣x∣≥1\alphax2+β:∣x∣<1\begin{cases}\dfrac{1}{x2} & : \left|x\right| ≥ 1 \\ \alphax^{2} + \beta& : \left|x\right| < 1\end{cases}.\right)Iff(x)If f \left(x\right) is continuous and differentiable at any point, then

Options

  1. Aα=2,β=−1\alpha = 2, \beta = - 1
  2. Bα=−1,β=2\alpha = - 1, \beta = 2
  3. Cα=1,β=0\alpha = 1, \beta = 0
  4. Dα=−2,β=3\alpha = - 2, \beta = 3

Correct answer

B. α=−1,β=2\alpha = - 1, \beta = 2

Step-by-step solution

The given function is clearly continuous at all points except possibly at x=±1.x = \pm 1 .
For f(x)f\left(x\right) to be continuous at x=1,x = 1, we must have
lim⁡x→1−f(x)=lim⁡x→1+f(x)=f(1)\lim_{x \to {1}^{-}}f\left(x\right) = \lim_{x \to {1}^{+}}f\left(x\right) = f\left(1\right)
⇒lim⁡x→1−αx2+β=lim⁡x→1+1x2⇒ \lim_{x \to {1}^{-}}\alpha{x}^{2} + \beta = \lim_{x \to {1}^{+}}\dfrac{1}{{x}^{2}}
⇒α+β=1⇒ \alpha + \beta = 1 … \left(1\right)<br/>Now,for<br />Now, forf\left(x\right)tobedifferentiableatto be differentiable atx = 1,wemusthave<br/>we must have<br />\lim_{x \to {1}^{-}}\dfrac{f\left(x\right) - f\left(1\right)}{x - 1} = \lim_{x \to {1}^{+}}\dfrac{f\left(x\right) - f\left(1\right)}{x - 1}<br/><br />⇒ \lim_{x \to {1}^{-}}\dfrac{\alpha{x}^{2} + \beta - 1}{x - 1} = \lim_{x \to {1}^{+}}\dfrac{\dfrac{1}{{x}^{2}} - 1}{x - 1}(∵α+β=1∴β−1=−α)\left(∵ \alpha + \beta = 1 ∴ \beta - 1 = - \alpha\right)
⇒lim⁡x→1−αx2−αx−1=lim⁡x→1+1x2−1x−1⇒ \lim_{x \to {1}^{-}}\dfrac{\alpha{x}^{2} - \alpha}{x - 1} = \lim_{x \to {1}^{+}}\dfrac{\dfrac{1}{{x}^{2}} - 1}{x - 1}
⇒lim⁡x→1−α(x+1)=lim⁡x→1+−2x3⇒2α=−2⇒ \lim_{x \to {1}^{-}}\alpha\left(x + 1\right) = \lim_{x \to {1}^{+}}\dfrac{- 2}{{x}^{3}} ⇒ 2\alpha = - 2
⇒α=−1⇒ \alpha = - 1
Putting α=−1\alpha = - 1 in \left(1\right),wegetwe get\beta = 2
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 NTA Abhyas JEE Main PYQs