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anonymous

  • 5 years ago

whats the integral of xe^(4-x) as x approaches infinity?

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  1. mathteacher1729
    • 5 years ago
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    \[\int_{}^{\infty} xe^{4-x}dx\] What is the lower limit? really can't do much without that.

  2. anonymous
    • 5 years ago
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    oops, sorry! 4

  3. mathteacher1729
    • 5 years ago
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    \[\int_{4}^{\infty} xe^{4-x}dx\] is that the problem?

  4. anonymous
    • 5 years ago
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    yes correct

  5. anonymous
    • 5 years ago
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    its not infinity or -infinity, but I cannot find out the answer

  6. anonymous
    • 5 years ago
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    Integrate by parts u=x and dv=e^4-x change infinity to t, then evaluate as a limit

  7. anonymous
    • 5 years ago
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    (as t goes to infinity)

  8. anonymous
    • 5 years ago
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    \[\lim_{4 \rightarrow \infty} -x e^{4-x} -e^{4-x} ?\]

  9. anonymous
    • 5 years ago
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    ? i have no idea...

  10. anonymous
    • 5 years ago
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    x--->infinity

  11. anonymous
    • 5 years ago
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    *

  12. anonymous
    • 5 years ago
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    Yep, you got the integral right. now sub in your upper and lower limits. Now you should have something with t in it ( y(t) ) Take the limit of this as t goes to infinity

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