Question

what's (x+40) dx?

Answer 1

i think youre missing part

Answer 2

ok ill post up what problem i am doing... http://www.webassign.net/cgi-bin/symimage.cgi?expr=int%20%5C%28x%20%2B%2040%5C%29%20sqrt%2880%20x%20%2B%20x%2A%2A2%29%20dx

Answer 3

x^2/2+40x+c

Answer 4

i knew it lol

Answer 5

????

Answer 6

there were parts missing ....

Answer 7

well i post the problem up and tell me how you would elevaulte indefinite ingrels

Answer 8

got it on paper and looking at it

Answer 9

\[\int\limits (x+40) \sqrt{80x+x^2} dx= what?\]

Answer 10

so simple... take x common inside the root

Answer 11

ok thanks...i factor out the u :\[du = 80+2x^2 du=2(x+40)....1/2du=(x+40)dx\]

Answer 12

but i dont know how to solve the x+40

Answer 13

x+40 cancels out; or rather is absorbed into the du/2

Answer 14

\[\frac{1}{2}\int \sqrt{u}\ du\]
is what you should end up with right?

Answer 15

or another way to see it:

\[\int \frac{(x+40)\sqrt{u}}{2(x+40)}du\]

Answer 16

yes but the answer i got was \[3/4(80x+x^2)^{3/2}+C\]

Answer 17

well can you show me how you would use it that way

Answer 18

and the online tells me otherwise

Answer 19

instead of just trying to solve for a part of dx; solve for dx outright and apply it in the integral to see what cancels.

u = 80x+x^2

du = (80+2x) dx

du/(80+2x) = dx


(x+40) sqrt(u)
{S} ------------ du
2(x+40)


sqrt(u)
{S} ----- du = (1/2) {S} sqrt(u) du
2

Answer 20

u^((1+2)/2) u^(3/2)
(1/2) {S} u^(1/2) du --> (1/2) ---------- = --------
(1+2)/2 2(3/2)


u^(3/2)
------- + C is what it simplifies to right?
3

Answer 21

you didnt flip over your bottom part

Answer 22

3/2 becomes 2/3

Answer 23

o man your right!!! ughhh!!!

Answer 24

so its 1/3(80x+x^2)^3/2 + C

Answer 25

yep

Answer 26

thanks so much for pointing that out

Answer 27

no prob ..