Practice: Limits

Calculus Level 2

Evaluate lim x 0 e 44 x 1 x 2 + 2 x \displaystyle \lim_{x \to 0} \frac{e^{44x} - 1}{x^2+2x} .


The answer is 22.

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5 solutions

Ryan Phua
Dec 16, 2013

Since directly substituting x = 0 x=0 into the expression gives us e 44 ( 0 ) 1 0 2 + 2 ( 0 ) = 0 0 \frac {e^{44(0)}-1}{0^2+2(0)} = \frac {0}{0} , we can use L'Hopital's rule and differentiate the numerator and the denominator of the fraction.

lim x 0 e 44 x 1 x 2 + 2 x = lim x 0 44 e 44 x 2 x + 2 = 44 e 0 2 ( 0 ) + 2 = 44 2 = 22 \lim_{x \to 0} {\frac {e^{44x}-1}{x^2+2x}} = \lim_{x \to 0} {\frac {44e^{44x}}{2x+2}} = \frac {44e^0}{2(0)+2} = \frac {44}{2} = \boxed{22}

I would rather choose to do it by dividing numerator and denominator with 44x and applying standard limits..:)

Kuladip Maity - 7 years, 5 months ago

oh that was easy

Asaduzzaman Hridhoy - 7 years, 5 months ago

by using L hospital rule we get ans as 1/2 isnt it

Anurag Parchuri - 7 years, 5 months ago

Would somebody explain to me why I get 44xe^(44x - 1) when I differentiate e^(44x) - 1 with the chain rule (ax^n -> anx^n-1), and not 44e^(44x)? Thanks :(

Michael Thornton - 7 years, 5 months ago
Cid Moraes
Dec 16, 2013

Is clear that the expression can be rewritten as e 44 x 1 x 2 + 2 x = e 44 x 1 44 x 44 x x 2 + 2 x \frac{\text{e}^{44x}-1}{x^2+2x}=\frac{\text{e}^{44x}-1}{44x}\cdot\frac{44x}{x^2+2x} so by the fundamental limit lim t 0 e t 1 t = 1 \lim_{t \to 0}\frac{\text{e}^t-1}{t} =1 we have e 44 x 1 44 x 44 x x 2 + 2 x = e 44 x 1 44 x 44 x + 2 1 44 2 = 22 \frac{\text{e}^{44x}-1}{44x}\cdot\frac{44x}{x^2+2x}=\frac{\text{e}^{44x}-1}{44x}\cdot\frac{44}{x+2} \to 1\cdot \frac{44}{2} =22

Clever

John M. - 7 years, 4 months ago
Ahaan Rungta
Dec 17, 2013

This is a 0 0 \dfrac {0}{0} form, so it is of an indeterminate form. So we use L'Hôpital's rule: lim x 0 ( e 44 x 1 x 2 + 2 x ) = lim x 0 ( 44 e 44 x 2 x + 2 ) = lim x 0 ( 22 e 44 x x + 1 ) = 22 e 0 0 + 1 = 22 . \begin{aligned} \lim_{x \to 0} \left( \dfrac {e^{44x} - 1}{x^2 + 2x} \right) &= \lim_{x \to 0} \left( \dfrac {44e^{44x}}{2x+2} \right) \\&= \lim_{x \to 0} \left( \dfrac {22e^{44x}}{x+1} \right) \\&= \dfrac {22 \cdot e^0}{0+1} = \boxed {22}. \end{aligned}

at first if you put x = 0 x=0 in the expression you get 0 0 \frac{0}{0} form, then applying l'hopital's rule i.e. differentiatiating the numerator and denominator we get 44 e 44 x 2 x + 2 \frac{44e^{44x}}{2x+2} , then put x=0 and you'll get 44 2 \frac {44}{2} i.e 22.

Sahir Ali
Dec 16, 2013

use L Hopitals rule just take derivative on numerator and denominator seperately and then apply limit remember donot use qoutient rule besta luck

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