Find limit of sin(x).sin^-1(x)/x^2 as x approaches 0

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You should get \frac{\frac{1}{\sqrt{1- x^2}}}{2x}- \frac{\sin(x)}{x^2\sqrt{1- x^2}}= \frac{1}{2x^3\sqrt{1- x^2}}- \frac{\sin(x)}{x^2\sqrt{1- x^2}}.At x= 0, that is \frac{1}{0}- 0= infinity.
  • #1
DryRun
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Homework Statement


Find limit of sin(x).sin^-1(x)/x^2 as x approaches 0

Homework Equations


Maybe L'Hopital's rule.

The Attempt at a Solution


First, i put in zero, and got the indeterminate form 0/0
So, i used L'Hopital's rule and got this:

[cosx.sin^-1(x) + sinx.-sin^-2(x).cosx]/2x

And again when putting zero, i get [1/0 + 0]/0 = infinity/0
So i tried to differentiate again, but it's become so big, i don't know what's what in my copybook. Help!
 
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  • #2
Write out the function as

[tex]\frac{sin(x)}{x}\frac{sin^{-1}(x)}{x}[/tex].

You know the limit of the first fraction. Apply L'Hospital to the second one.

ehild
 
  • #3
sharks said:

Homework Statement


Find limit of sin(x).sin^-1(x)/x^2 as x approaches 0


Homework Equations


Maybe L'Hopital's rule.


The Attempt at a Solution


First, i put in zero, and got the indeterminate form 0/0
So, i used L'Hopital's rule and got this:

[cosx.sin^-1(x) + sinx.-sin^-2(x).cosx]/2x

And again when putting zero, i get [1/0 + 0]/0 = infinity/0
"infinity/0" is NOT an indeterminate form! That would tell you the limit is infinity.

However, you seem to be thinking that [tex]sin^{-1}(x)[/tex] means [tex]1/sin(x)[/tex]. That's clearly NOT the case here since, if it were, "[itex]sin(x)sin^{-1}(x)[/itex]" would just be 1 and [itex]sin(x)sin^{-1}(x)/x^2[/itex] would be just [itex]1/x^2[/itex] which does go to infinity.

However, here, [itex]sin^{-1}(x)[/itex] is the arcsine, the inverse function to sine. The derivative of arcsin(x) is [itex]1/\sqrt{1- x^2}[/itex].

So i tried to differentiate again, but it's become so big, i don't know what's what in my copybook. Help!
 

1. What is the limit of sin(x).sin^-1(x)/x^2 as x approaches 0?

The limit of sin(x).sin^-1(x)/x^2 as x approaches 0 is equal to 1/2.

2. How do you find the limit of sin(x).sin^-1(x)/x^2 as x approaches 0?

To find the limit of sin(x).sin^-1(x)/x^2 as x approaches 0, we can use the L'Hopital's Rule or the trigonometric identity sin(x)/x = 1 as x approaches 0.

3. Why is the limit of sin(x).sin^-1(x)/x^2 as x approaches 0 equal to 1/2?

This limit is equal to 1/2 because as x approaches 0, the value of sin(x)/x approaches 1. Therefore, the limit becomes sin^-1(x)/x, which can be rewritten as (sin^-1(x)/x) * (1/x). As x approaches 0, the first term becomes 1 and the second term becomes infinity, resulting in a limit of 1/2.

4. Can this limit be evaluated using any other methods?

Yes, this limit can also be evaluated using the Taylor Series expansion for sin^-1(x) and x^2 as x approaches 0. In this method, we can also get a limit of 1/2.

5. What is the significance of finding the limit of sin(x).sin^-1(x)/x^2 as x approaches 0?

Finding the limit of this expression helps us understand the behavior of trigonometric functions and how they approach a certain value as the input approaches a particular point. It also has applications in calculus and other branches of mathematics.

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