Integral of 1/2^x | Homework Solution

  • Thread starter Maddie1609
  • Start date
  • Tags
    Integral
In summary: I'm tired. My brain is not working so well. I'll be back tomorrow. Goodnight.In summary, using the substitution u = ln 2x, the integral of 1/2x from 1 to infinity is equal to -e-x ln 2/ln 2, or -2-x/ln2.
  • #1
Maddie1609
81
11

Homework Statement


1 1/2x

Homework Equations



2-x = (eln 2)-x

Could possibly be relevant, I don't know.

The Attempt at a Solution



y = 2-x

ln y = -x ln 2

1/y dy/dx = -ln 2 -x/2

...
 
Physics news on Phys.org
  • #2
Maddie1609 said:

Homework Statement


1 1/2x

Homework Equations



2^-x = (eln 2)-x
Better is [itex]2^{-x}= e^{ln(2^{-x})}= e^{x ln(2)}[/itex]

Could possibly be relevant, I don't know.

The Attempt at a Solution



y = 2-x

ln y = -x ln 2

1/y dy/dx = -ln 2 -x/2

...
 
  • #3
Maddie1609 said:

Homework Equations



2-x = (eln 2)-x

Could possibly be relevant, I don't know.
Quite relevant, try to build on that.

ETA: never mind, didn't see the previous post.
 
Last edited:
  • #4
Samy_A said:
Quite relevant, try to build on that.

ETA: never mind, didn't see the previous post.

∫(1/2x) dx = ∫(1/ex ln 2) dx

u = ln 2 x → du = ln 2 dx

1/ln 2 ∫ du/eu = ln eu / ln 2 = ln ex ln 2 / ln 2 = x ln 2/ln2 = x

Okay, what did I do wrong?o_O

Edit: I was thinking of u'/ln u, my bad!

1/ln 2 ∫ e-u du = -e-u/ln 2 = -e-x ln 2/ln 2 = -2-x/ln2

Is this correct?
 
Last edited:
  • #5
HallsofIvy said:
Better is [itex]2^{-x}= e^{ln(2^{-x})}= e^{x ln(2)}[/itex]
Wouldn't that be e-x ln 2?
 
  • #6
Maddie1609 said:
∫(1/2x) dx = ∫(1/ex ln 2) dx

u = ln 2 x → du = ln 2 dx

1/ln 2 ∫ du/eu = ln eu / ln 2
You lost me in this last equality, I guess here something is wrong.

Also, don't forget to adapt the limits of your definite integral when you apply the substitution (not that I think that you really need that substitution).
 
  • #7
Maddie1609 said:
Edit: I was thinking of u'/ln u, my bad!

1/ln 2 ∫ e-u du = -e-u/ln 2 = -e-x ln 2/ln 2 = -2-x/ln2

Is this correct?
Yes, this is correct for the indefinite integral.
 
  • Like
Likes Maddie1609
  • #8
Samy_A said:
You lost me in this last equality, I guess here something is wrong.

Also, don't forget to adapt the limits of your definite integral when you apply the substitution (not that I think that you really need that substitution).
Yes I made an edit on my post, I was thinking of u'/ln u. I think I've got it now.

Screenshot_2015-10-25-14-23-21.png
 
  • #9
Maddie1609 said:
Wouldn't that be e-x ln 2?
Yes. Thanks.
 
  • Like
Likes Maddie1609

FAQ: Integral of 1/2^x | Homework Solution

1. What is the formula for the integral of 1/2^x?

The formula for the integral of 1/2^x is -(2^x ln(2))/ln(2) + C, where C is the constant of integration.

2. How do you solve the integral of 1/2^x?

To solve the integral of 1/2^x, you can use the formula -(2^x ln(2))/ln(2) + C or you can use integration by substitution. Let u = 2^x and du = 2^x ln(2) dx. Then the integral becomes ∫1/u du, which is simply ln(u) + C. Substituting back in for u, we get -(2^x ln(2))/ln(2) + C.

3. What is the derivative of 1/2^x?

The derivative of 1/2^x is -ln(2) * 1/2^x * (2^x ln(2)) = -ln(2) * 2^x * ln(2) = -2^x * ln^2(2).

4. How does the graph of the integral of 1/2^x compare to the original function?

The graph of the integral of 1/2^x is the area under the curve of the original function. This means that the graph of the integral will always be increasing, while the graph of 1/2^x can either be increasing or decreasing depending on the value of x. Additionally, the integral will approach a horizontal asymptote at y = 0, while the original function will approach a vertical asymptote at x = 0.

5. Can the integral of 1/2^x be solved using other methods?

Yes, the integral of 1/2^x can also be solved using integration by parts or using the power rule for integration. However, using integration by substitution is usually the most efficient method for this particular integral.

Similar threads

Back
Top