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JEE Main 20199 AprilEvening Shift
Exam
JEE Main
Year
2019
Date
9 April
Shift
Evening Shift
Subject
Mathematics
Chapter
Continuity and Differentiability

JEE Main 2019 · 9 April · Evening Shift · Mathematics · Continuity and Differentiability

If the function f(x) = \ array ll a|π - x| + 1, x ≤ 5 b|x - π| + 3,...

If the function f\left(x\right) = \left\{a∣π−x∣+1,x≤5b∣x−π∣+3,x>5\begin{array}{ll}a\left|\pi - x\right| + 1, x \le 5 \\ b\left|x - \pi\right| + 3, x > 5\end{array}\right) is continuous atx = 5, then the value of a−ba - b is:

Options

  1. A25−π\dfrac{2}{5 - \pi}
  2. B−2π+5\dfrac{- 2}{\pi + 5}
  3. C2π+5\dfrac{2}{\pi + 5}
  4. D2π−5\dfrac{2}{\pi - 5}

Correct answer

A. 25−π\dfrac{2}{5 - \pi}

Step-by-step solution

For continuity at x=5x = 5

lim⁡x→5+f(x)=lim⁡x→5−f(x)=f(5)\lim_{x \to {5}^{+}}f\left(x\right) = \lim_{x \to {5}^{-}}f\left(x\right) = f\left(5\right)

⇒lim⁡x→5+(b∣x−π∣+3)=lim⁡x→5−a(∣π−x∣+1)=a(5−π)+1⇒ \lim_{x \to {5}^{+}}\left(b\left|x - \pi\right| + 3\right) = \lim_{x \to {5}^{-}}a\left(\left|\pi - x\right| + 1\right) = a\left(5 - \pi\right) + 1

We know that \left|x\right| = \left\{{x,x≥0−x,x<0\begin{cases}x, & x \ge 0 \\ - x, & x < 0\end{cases}\right)

⇒b(5−π)+3=a(5−π)+1=a(5−π)+1⇒ b\left(5 - \pi\right) + 3 = a\left(5 - \pi\right) + 1 = a\left(5 - \pi\right) + 1

⇒b(5−π)+3=a(5−π)+1⇒ b\left(5 - \pi\right) + 3 = a\left(5 - \pi\right) + 1

⇒3−1=a(5−π)−b(5−π)⇒ 3 - 1 = a\left(5 - \pi\right) - b\left(5 - \pi\right)

⇒(a−b)(5−π)=2⇒ \left(a - b\right)\left(5 - \pi\right) = 2

⇒a−b=25−π.⇒ a - b = \dfrac{2}{5 - \pi} .

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