Inspired by Ashish Siva

Calculus Level 3

L = lim x 0 sin x x \large L = \lim_{x\to0} \left \lfloor \dfrac{ \sin x} x \right \rfloor

Find the value of L L .

Notation : \lfloor \cdot \rfloor denotes the floor function .


Inspiration .

1 2 \dfrac12 None of these choices 0 0 1 1 Limit does not exist

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1 solution

Chew-Seong Cheong
May 19, 2016

L = lim x 0 sin x x By Maclaurin series = lim x 0 1 x ( x x 3 3 ! + x 5 5 ! . . . ) = lim x 0 1 x 2 3 ! + x 4 5 ! . . . As the infinite polynomial p ( x ) is even. lim x 0 p ( x ) = lim x 0 + p ( x ) = L = 0 Since p ( x ) < 1 \begin{aligned} L & = \lim_{x \to 0} \left \lfloor \frac{\color{#3D99F6}{\sin x}}{x} \right \rfloor \quad \quad \small \color{#3D99F6}{\text{By Maclaurin series}} \\ & = \lim_{x \to 0} \left \lfloor \frac{1}{x} \color{#3D99F6}{\left(x - \frac{x^3}{3!} + \frac{x^5}{5!} - ... \right)} \right \rfloor \\ & = \lim_{x \to 0} \left \lfloor \color{#3D99F6}{1 - \frac{x^2}{3!} + \frac{x^4}{5!} - ... } \right \rfloor \quad \quad \small \color{#3D99F6}{\text{As the infinite polynomial } p(x) \text{ is even.} \implies \lim_{x \to 0^-} \left \lfloor p(x) \right \rfloor = \lim_{x \to 0^+} \left \lfloor p(x) \right \rfloor = L} \\ & = \boxed{0} \quad \quad \small \color{#3D99F6}{\text{Since } p(x) < 1} \end{aligned}

Nice solution ...+1

Sabhrant Sachan - 5 years ago

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