Show that ##\sin(\arctan x) < x < \tan(\arcsin x)##

In summary, the given problem shows that for 0 < x < 1, the inequality sin(arctan(x)) < x < tan(arcsin(x)) holds true. Additionally, the attempt to write an expression for tan(arcsin(x)) is not necessary as it can be compared directly to arctan(x) and arcsin(x) with x.
  • #1
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The problem
For ##0 < x < 1 ## . Show that
$$ \sin(\arctan x) < x < \tan(\arcsin x) $$

The attempt

I know that ## \sin x < x < \tan x ## is true for ## 0 < x < \ \pi / 2 ##

220px-Sinxoverx.png
x - is by definition the length DA (in radians)

I draw a right triangle with sides x and 1 and with hypotenuse ## \sqrt{x^2+1} ##

## \sin v = \frac{x}{\sqrt{x^2+1}} ##

## \tan v = \frac{x}{1} \Rightarrow v = \arctan \ x ##

## \sin (\arctan \ x) = \frac{x}{\sqrt{x^2+1}} ##I am trying to write an expression for ## \tan(\arcsin(x)) ##

## \sin v = \frac{x}{\sqrt{x^2+1}} \Rightarrow v = \arcsin \left( \frac{x}{\sqrt{x^2+1}} \right)##

## \tan v = x \Rightarrow \tan \left( \arcsin \left( \frac{x}{\sqrt{x^2+1}} \right) \right) = x##

But I fail. Please Help me write an expression for ## \tan(\arcsin(x)) ##.
 
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  • #2
I don't think this is necessary. You can compare arctan(x) and arcsin(x) with x.
 

Related to Show that ##\sin(\arctan x) < x < \tan(\arcsin x)##

1. What is the significance of the equation ##\sin(\arctan x) < x < \tan(\arcsin x)##?

The equation ##\sin(\arctan x) < x < \tan(\arcsin x)## provides a relationship between the trigonometric functions sine (##\sin##), tangent (##\tan##), and inverse trigonometric functions arctangent (##\arctan##) and arcsine (##\arcsin##). This relationship can be used to find the values of these functions for a given value of x.

2. How do you prove that ##\sin(\arctan x) < x < \tan(\arcsin x)## is true?

To prove that ##\sin(\arctan x) < x < \tan(\arcsin x)## is true, we can use the fact that ##\sin(\theta) < \theta < \tan(\theta)## for all values of ##\theta## between 0 and ##\frac{\pi}{2}##. This can be shown by plotting the graphs of these functions and observing their behavior in this range. Then, by substituting ##\arctan x## for ##\theta## and using the properties of inverse trigonometric functions, we can prove the given inequality.

3. What is the domain of the equation ##\sin(\arctan x) < x < \tan(\arcsin x)##?

The domain of the equation ##\sin(\arctan x) < x < \tan(\arcsin x)## is all real numbers except for x = 0, as the arctangent function is undefined at x = 0 and the arcsine function is undefined for values outside of [-1, 1].

4. Can this equation be used to find the values of inverse trigonometric functions?

Yes, this equation can be used to find the values of inverse trigonometric functions. By rearranging the equation, we can solve for the arctangent or arcsine of x, depending on which function we are interested in. This can be useful in applications where we need to find the angle corresponding to a given value of a trigonometric function.

5. Are there any conditions in which the inequality ##\sin(\arctan x) < x < \tan(\arcsin x)## does not hold?

Yes, there are a few conditions in which the inequality ##\sin(\arctan x) < x < \tan(\arcsin x)## does not hold. These include when x is outside of the domain of the equation, or when x is negative and the inequality is reversed. Additionally, the inequality may not hold for certain values of x that result in undefined trigonometric functions or when x is close to the boundaries of the domain.

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