Let's do some calculus! (44)

Calculus Level 4

lim x x 100 ln ( x ) e x arctan ( π 3 + sin x ) = ? \large \displaystyle \lim_{x \to \infty} \dfrac{x^{100} \ln(x)}{e^x \arctan \left( \frac \pi3 + \sin x \right)} \ = \ ?


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The answer is 0.

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2 solutions

Aareyan Manzoor
Jun 12, 2017

this can be done by squeezing: lim x x 101 e x arctan ( π 3 + sin x ) lim x x 100 ln ( x ) e x arctan ( π 3 + sin x ) lim x x 100 e x arctan ( π 3 + sin x ) \lim_{x \to \infty} \dfrac{x^{101}}{e^x \arctan \left( \frac \pi3 + \sin x \right)} \geq \lim_{x \to \infty} \dfrac{x^{100}\ln(x)}{e^x \arctan \left( \frac \pi3 + \sin x \right)}\geq \lim_{x \to \infty} \dfrac{x^{100}}{e^x \arctan \left( \frac \pi3 + \sin x \right)} since 1 sin ( x ) 1 -1\leq\sin(x)\leq 1 , arctan ( π 3 1 ) arctan ( π 3 + sin x ) arctan ( π 3 + 1 ) \arctan \left( \frac \pi3 -1 \right)\geq\arctan \left( \frac \pi3 + \sin x \right)\geq\arctan \left( \frac \pi3 + 1 \right) since arctangent is monotone in that range. but these are constants, so 0 = lim x x 100 e x arctan ( π 3 + 1 ) lim x x 100 e x arctan ( π 3 + sin x ) lim x x 100 e x arctan ( π 3 1 ) = 0 lim x x 100 e x arctan ( π 3 + sin x ) = 0 0=\lim_{x \to \infty} \dfrac{x^{100}}{e^x \arctan \left( \frac \pi3 +1 \right)}\geq \lim_{x \to \infty} \dfrac{x^{100}}{e^x \arctan \left( \frac \pi3 + \sin x \right)}\geq \lim_{x \to \infty} \dfrac{x^{100}}{e^x \arctan \left( \frac \pi3 - 1 \right)}=0\to \lim_{x \to \infty} \dfrac{x^{100}}{e^x \arctan \left( \frac \pi3 + \sin x \right)}=0 similarly lim x x 101 e x arctan ( π 3 + sin x ) = 0 0 lim x x 100 ln ( x ) e x arctan ( π 3 + sin x ) 0 lim x x 100 ln ( x ) e x arctan ( π 3 + sin x ) = 0 \lim_{x \to \infty} \dfrac{x^{101}}{e^x \arctan \left( \frac \pi3 + \sin x \right)}=0\to 0\geq\lim_{x \to \infty} \dfrac{x^{100}\ln(x)}{e^x \arctan \left( \frac \pi3 + \sin x \right)}\geq 0\\\lim_{x \to \infty} \dfrac{x^{100}\ln(x)}{e^x \arctan \left( \frac \pi3 + \sin x \right)}=\boxed{0}

Hana Wehbi
Mar 11, 2017

Regardless of the heavy stuff this problem has, look at the bottom, we have e x e^x . Plugging into e x \infty \text {into}\ e^x yields an infinity denominator, thus the answer is 0 because N = 0 \frac{N}{\infty}=0 Not a solution, just an idea that came to mind.

But numerator also tends to infinity as x--->infinity.

So u have to show that numerator < denominator. for large values of x.

Sudhamsh Suraj - 4 years, 3 months ago

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Yes, we need lhopital rule here to solve it.

Hana Wehbi - 4 years, 3 months ago

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