how do i integrate this?

nevinsmith · 2011-07-23 22:44:06

xSin(x^3)

pls help!

gAr · 2011-07-23 23:01:25

Hi,

Are you sure it's sin(x^3) and not sin(x)^3 ?

If it's sin(x^3) , CAS gives the answer in terms of gamma function.

bobbym · 2011-07-23 23:29:12

Hi nevinsmith;

gAr is right! have you posted the correct problem?

nevinsmith · 2011-07-23 23:56:07

oh wait i missed out the definite integrals, its between pi and 0

the answers says 2pi/3

bobbym · 2011-07-23 23:59:20

Hi nevinsmith;

I am not getting that for that integral:

Is this what you want?

It should be this:

nevinsmith · 2011-07-24 00:03:06

no it's not x(sinx)^3 or xsin^3x

it's xsin(x^3) brackets present in the question and x^3 inside the bracket

nevinsmith · 2011-07-24 00:04:21

could be a print error though

does the other one work out to be 2pi/3?

bobbym · 2011-07-24 00:05:17

Hi;

Something is wrong when it is x sin(x)^3 we get the answer you want. The other integral does not. Must be a typo in the question.

gAr · 2011-07-24 00:08:08

Yes, it's a print error!

The second integral shown by bobbym evaluates to 2*pi/3.

nevinsmith · 2011-07-24 00:19:12

oh right, but i still can't solve it

how do i integrate x(sinx)^3

techniques i've taught are- integration by parts, substitution, trignometric substitution, partial fractions and i think thats it

bobbym · 2011-07-24 00:21:37

Integration by parts should do it.

gAr · 2011-07-24 00:22:25

Hi,

Use:

nevinsmith · 2011-07-24 00:31:22

hi gar and bobbym thanks for helpin guys

I still can't do it

can you please show me step by step how to integrate?
using integration by parts? i can't seem to get rid of the integral it keeps getting bigger and bigger

do i set u' as (sinx)^3 or as x

anonimnystefy · 2011-07-24 00:33:49

hi nevinsmith

i think it should be u=x and dv=(sinx)^3 dx

nevinsmith · 2011-07-24 00:44:53

This is what i can get up to

int xSinx^3 dx

set u=x u'=1

v'=sinx^3 integrate, v= cosx-1/3cosx^3

then integrate by parts

=xcosx-1/3xcosx^3 - int (cosx-1/3cosx^3)

i can't et rid of the integral!!

please help me!

gAr · 2011-07-24 00:53:48

Hi,

Here it is:

nevinsmith · 2011-07-24 00:56:53

Hi Gar,

wow thank you so much!
thats so genious i would never think of that lol

thanks for the solution man!

gAr · 2011-07-24 01:03:40

Hi nevinsmith,

You're welcome!

The properties of definite integrals are very useful, make most use of it.

Math Is Fun Forum

#1 2011-07-23 22:44:06

how do i integrate this?

#2 2011-07-23 23:01:25

Re: how do i integrate this?

#3 2011-07-23 23:29:12

Re: how do i integrate this?

#4 2011-07-23 23:56:07

Re: how do i integrate this?

#5 2011-07-23 23:59:20

Re: how do i integrate this?

#6 2011-07-24 00:03:06

Re: how do i integrate this?

#7 2011-07-24 00:04:21

Re: how do i integrate this?

#8 2011-07-24 00:05:17

Re: how do i integrate this?

#9 2011-07-24 00:08:08

Re: how do i integrate this?

#10 2011-07-24 00:19:12

Re: how do i integrate this?

#11 2011-07-24 00:21:37

Re: how do i integrate this?

#12 2011-07-24 00:22:25

Re: how do i integrate this?

#13 2011-07-24 00:31:22

Re: how do i integrate this?

#14 2011-07-24 00:33:49

Re: how do i integrate this?

#15 2011-07-24 00:44:53

Re: how do i integrate this?

#16 2011-07-24 00:53:48

Re: how do i integrate this?

#17 2011-07-24 00:56:53

Re: how do i integrate this?

#18 2011-07-24 01:03:40

Re: how do i integrate this?

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