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QJEEM22Ma12e6: JEE Main 2022 Mathematics - Class 12 JEEM22Ma12e6 Solution: Let for some . Then the value of is :

Let β=lim⁡x→0αx−(e3x−1)αx(e3x−1)\beta=\mathop {\lim }\limits_{x \to 0} \frac{\alpha x-\left(e^{3 x}-1\right)}{\alpha x\left(e^{3 x}-1\right)} for some α∈R\alpha \in \mathbb{R} . Then the value of α+β\alpha+\beta is :

Multiple Choice Options

  • A 145\frac{14}{5}
  • B 32\frac{3}{2}
  • C 52\frac{5}{2}
  • D 72\frac{7}{2}

Step-by-Step Verified Solution

β=lim⁡x→0αx−(e3x−1)αx(e3x−1), α∈R\beta = \mathop {\lim }\limits_{x \to 0} {{\alpha x - ({e^{3x}} - 1)} \over {\alpha x({e^{3x}} - 1)}},\,\alpha \in R

=lim⁡x→0α3−(e3x−13x)αx(e3x−13x)= \mathop {\lim }\limits_{x \to 0} {{{\alpha \over 3} - \left( {{{{e^{3x}} - 1} \over {3x}}} \right)} \over {\alpha x\left( {{{{e^{3x - 1}}} \over {3x}}} \right)}}

So, α=3\alpha = 3 (to make independent form)

β=lim⁡x→01−(e3x−13x)3x=1−(3x+9x22 + ......)3x3x\beta = \mathop {\lim }\limits_{x \to 0} {{1 - \left( {{{{e^{3x}} - 1} \over {3x}}} \right)} \over {3x}} = {{1 - {{\left( {3x + {{9{x^2}} \over 2}\, + \,......} \right)} \over {3x}}} \over {3x}}

=−(92x2+(3x)331 + ....)9x2=−12= {{ - \left( {{9 \over 2}{x^2} + {{{{(3x)}^3}} \over {31}}\, + \,....} \right)} \over {9{x^2}}} = {{ - 1} \over 2}

∴\therefore α+β=3−12=52\alpha + \beta = 3 - {1 \over 2} = {5 \over 2}

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