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JEE Main 202120 JulyEvening Shift
Exam
JEE Main
Year
2021
Date
20 July
Shift
Evening Shift
Subject
Mathematics
Chapter
Limits

JEE Main 2021 · 20 July · Evening Shift · Mathematics · Limits

If _ x → 0 [ e ^ x - β _ e ( 1 + x ) + γ x ^ 2 e ^ - x x ^ 2 x ] =...

If lim⁡x→0[\alphaxex−βlog⁡e(1+x)+γx2e−xxsin⁡2x]=10,α,β,γ∈R\lim_{x \to 0}\left[\dfrac{\alphax{e}^{x} - \beta{\log}_{e} ( 1 + x ) + \gamma{x}^{2}{e}^{- x}}{x\sin^{2}x}\right] = 10, \alpha, \beta, \gamma \in R, then the value of α+β+γ\alpha + \beta + \gamma is __________.

Correct answer

0

Step-by-step solution

We have,

lim⁡x→0[\alphaxex−βlog⁡e(1+x)+γx2e−xxsin⁡2x]=10\lim_{x \to 0}\left[\dfrac{\alphax{e}^{x} - \beta{\log}_{e} ( 1 + x ) + \gamma{x}^{2}{e}^{- x}}{x\sin^{2}x}\right] = 10

⇒lim⁡x→0[\alphax(1+x+x22!+..)−β(x−x22+x33−...)+γx2(1−x+x22!−..)x3(sin⁡2xx2)]=10⇒ \lim_{x \to 0}\left[\dfrac{\alphax\left(1 + x + \dfrac{{x}^{2}}{2 !} + . .\right) - \beta\left(x - \dfrac{{x}^{2}}{2} + \dfrac{{x}^{3}}{3} - . . .\right) + \gamma{x}^{2}\left(1 - x + \dfrac{{x}^{2}}{2 !} - . .\right)}{{x}^{3}\left(\dfrac{\sin^{2}x}{{x}^{2}}\right)}\right] = 10

⇒lim⁡x→0[\alphax(1+x+x22)−β(x−x22+x33)+γx2(1−x)x3]=10⇒ \lim_{x \to 0}\left[\dfrac{\alphax\left(1 + x + \dfrac{{x}^{2}}{2}\right) - \beta\left(x - \dfrac{{x}^{2}}{2} + \dfrac{{x}^{3}}{3}\right) + \gamma{x}^{2}\left(1 - x\right)}{{x}^{3}}\right] = 10

Neglecting higher powers.

lim⁡x→0x(α−β)+x2(α+β2+γ)+x3(α2−β3−γ)x3=10\lim_{x \to 0}\dfrac{x ( \alpha - \beta ) + {x}^{2}\left(\alpha + \dfrac{\beta}{2} + \gamma\right) + {x}^{3}\left(\dfrac{\alpha}{2} - \dfrac{\beta}{3} - \gamma\right)}{{x}^{3}} = 10

For limit to exist

α−β=0\alpha - \beta = 0

α+β2+γ=0\alpha + \dfrac{\beta}{2} + \gamma = 0

α2−β3−γ=10…(i)\dfrac{\alpha}{2} - \dfrac{\beta}{3} - \gamma = 10 \ldots \left(i\right)

β=α,γ=−3α2\beta = \alpha, \gamma = - \dfrac{3\alpha}{2}

Putting in \left(i\right),weget</p><p>, we get</p><p>\dfrac{\alpha}{2} - \dfrac{\alpha}{3} + \dfrac{3\alpha}{2} = 10</p><p></p><p>⇒ \dfrac{\alpha}{6} + \dfrac{3\alpha}{2} = 10</p><p></p><p>⇒ \dfrac{\alpha + 9\alpha}{6} = 10</p><p></p><p>⇒ \alpha = 6</p><p>Hence,</p><p></p><p>Hence,</p><p>\alpha = 6, \beta = 6, \gamma = - 9</p><p></p><p>⇒ \alpha + \beta + \gamma = 3

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