Fractional mod!

Geometry Level 4

1 x 1 = x + sin x \large \left| \dfrac{1}{|x|-1}\right| = x+ \sin x

Find number of real values of x x satisfying above equation.

2 6 8 4 3 1 none of them

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Chew-Seong Cheong
Dec 15, 2015

1 x 1 = x + sin x 1 x 1 x = sin x 1 1 x 1 x 1 \left| \dfrac{1}{|x|-1} \right| = x + \sin x \quad \Rightarrow \left| \dfrac{1}{|x|-1} \right| - x = \sin x \quad \Rightarrow -1 \le \left| \dfrac{1}{|x|-1} \right| - x \le 1

Let f ( x ) = 1 x 1 x f(x) = \left| \dfrac{1}{|x|-1} \right| - x and consider it for x < 1 , 1 x < 0 , 0 x < 1 x < -1, \quad -1 \le x < 0, \quad 0 \le x < 1 and x 1 x \ge 1 .

f ( x ) = { 1 x 1 x [ 3 , ) for x < 1 1 x + 1 x ( 1 , ) for 1 x < 0 1 1 x x [ 1 , ) for 0 x < 1 1 x 1 x ( , ) for x 1 f(x) = \begin{cases} \dfrac{1}{-x-1} - x & \in [3,\infty) & \text{for } x <-1 \\ \dfrac{1}{x+1} - x & \in (1,\infty) & \text{for } -1 \le x <0 \\ \dfrac{1}{1-x} - x & \in [1,\infty) & \text{for } 0 \le x < 1 \\ \dfrac{1}{x-1} - x & \in (-\infty,\infty) & \text{for } x \ge 1 \end{cases}

1 1 x 1 x 1 \Rightarrow -1 \le \left| \dfrac{1}{|x|-1} \right| - x \le 1 when x 1 x \ge 1 and actually when 2 x 2 \sqrt{2} \le x \le 2 , and we have:

\(\begin{array} {} \text{When } x = \sqrt{2}, & f(\sqrt{2}) = 1 > \sin \sqrt{2} = 0.9878 \\ \text{When } x = 2, & f(2) = -1 < \sin 2 = 0.9093 \end{array} \)

Since 2 2 = 0.1865 π 2 - \sqrt{2} = 0.1865 \pi , there is only 1 \boxed{1} value of x x that satisfies the equation.

nice solution!!!

Atul Shivam - 5 years, 6 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...