1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Integrating e^7x

  1. Mar 30, 2012 #1
    1. The problem statement, all variables and given/known data

    S e^7x

    2. Relevant equations


    3. The attempt at a solution

    Ok so I am using U-substitution for this problem but I don't know what to do next.

    u = 7x, du = 7dx

    How do I integrate e^u*du?
  2. jcsd
  3. Mar 30, 2012 #2
    Try treating ∫eu du just as if it were ∫ex dx
  4. Mar 30, 2012 #3


    Staff: Mentor

    This is one of the easiest integrations!

    ##\int e^u~du = e^u + C##
  5. Mar 30, 2012 #4
    What happen's to du? Why does it dissapear in the solution?
  6. Mar 30, 2012 #5
    It disappears for the same reason when integrating something like ∫2x dx to get x2 + C
  7. Mar 30, 2012 #6
    I just want to point out, you are asking "how do I integrate"
    [tex]\int e^u \,du[/tex]

    Which implies a bit you MAY think that will give you the answer (you could have just omitted the 1/7 to be brief).

    But if you did miss it, since
    [tex]du =7dx \rightarrow dx = \frac{du}{7}[/tex]
    When you replace dx in the original integral with du/7 and 7x in the original integral with u, you get
    [tex]\int e^u \frac{du}{7}=\frac{1}{7} \int e^u \, du[/tex]
    Last edited: Mar 30, 2012
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook