Question

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

Answer 1

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

Answer 2

oops, sorry! 4

Answer 3

\[\int_{4}^{\infty} xe^{4-x}dx\] is that the problem?

Answer 4

yes correct

Answer 5

its not infinity or -infinity, but I cannot find out the answer

Answer 6

Integrate by parts u=x and dv=e^4-x
change infinity to t, then evaluate as a limit

Answer 7

(as t goes to infinity)

Answer 8

\[\lim_{4 \rightarrow \infty} -x e^{4-x} -e^{4-x} ?\]

Answer 9

? i have no idea...

Answer 10

x--->infinity

Answer 11

*

Answer 12

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