Limit Problem involving L'Hopital's Rule

Calculus Level 1

lim x ln 2 e x 2 x ln ( 2 ) = ? \lim_{x\to\ln2} \dfrac{e^x - 2}{x - \ln(2)} = \, ?


The answer is 2.

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2 solutions

James Watson
Aug 24, 2020

Since plugging in ln ( 2 ) \ln(2) here gives us a 0 0 \cfrac{0}{0} indeterminate form, we can use L'Hopital's Rule and differentiate the top and bottom: lim x ln ( 2 ) e x 2 x ln ( 2 ) lim x ln ( 2 ) d d x ( e x 2 ) d d x ( x ln ( 2 ) ) = lim x ln ( 2 ) e x 1 = lim x ln ( 2 ) e x = 2 \begin{aligned} \lim\limits_{x \to \ln(2)} \frac{e^x - 2}{x-\ln(2)} \implies \lim\limits_{x \to \ln(2)} \frac{\frac{d}{dx}(e^x - 2)}{\frac{d}{dx}(x-\ln(2))} &= \lim\limits_{x \to \ln(2)} \frac{e^x}{1} \\ &= \lim\limits_{x \to \ln(2)} e^x \\ &= \green{\boxed{2}} \end{aligned}

Chew-Seong Cheong
Aug 23, 2020

L = lim x ln 2 e x 2 x ln 2 A 0/0 case, L’H o ˆ pital’s rule applies = lim x ln 2 e x 1 Differentiate up and down w.r.t. x = e ln 2 = 2 \begin{aligned} L & = \lim_{x \to \ln 2} \frac {e^x - 2}{x - \ln 2} & \small \blue{\text{A 0/0 case, L'Hôpital's rule applies}} \\ & = \lim_{x \to \ln 2} \frac {e^x}1 & \small \blue{\text{Differentiate up and down w.r.t. }x} \\ & = e^{\ln 2} = \boxed 2 \end{aligned}


Reference: L'Hôpital's rule

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