Maths Olympiad Prep

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Algebra Difficulty 3.4 AMC 10/12 Find the answer

The number of real solutions to the equation x100=sinx\dfrac{x}{100}=\sin x is

Pick one

Solution

The answer to this problem is the number of intersections between the graph of f(x)=sinxf(x) = \sin x and f(x)=1100x.f(x) = \frac{1}{100}x. We can do the right side of the coordinate plane first. Each cycle of the sine wave, consisting of 2π, will have 2 intersections (From the positive part of the sine wave) The line f(x)=1100xf(x) = \frac{1}{100}x will consist of 16 cycles plus a little bit extra for xx from 1 to 100. However, the extra is not complete enough to have any intersection at all. Thus, the number of intersections is 216=32.2 \cdot 16 = 32. Because of symmetry, we can multiply by two to account for the left side, and subtract one because of the origin. So the answer is 3221=(C) 63.32 \cdot 2 - 1 = \textbf{(C)}\ 63.
https://www.desmos.com/calculator/z6edqwu1kx - Graph

~Eric X

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.