Homework Help: Need help with this

1. Jan 18, 2009

Dell

need urgent help with this

any ideas will be appreciated

$$\int$$x2(1-5x2)10dx

tried all kinds of things, what i now think needs to be done is to change the differential to d(1-5x2) so that i wont have to open the (1-5x2)10 which i really dont want to nor do i think i am expected to.

d(1-5x2)=-10xdx.... not really helping me :(

2. Jan 18, 2009

Staff: Mentor

Re: need urgent help with this

I tried several approaches, among them substitution and integration by parts, but didn't seem to get anywhere with either of these.

Another approach that seems promising is a trig substitution, using x = 1/sqrt(5) * cos(theta).

Using this approach I was able to rewrite the integral as
$$-1/25 \int cos^2(\theta) sin^{21}(\theta)d\theta$$
This could be rewritten as two integrals, both in powers of sin(theta). At that point, I would use a table of integrals.

This approach might be beyond your present capabilities, but it's the only one I can think of that leads anywhere.

3. Jan 18, 2009

Unco

Re: need urgent help with this

You could just expand the integrand using the binomial theorem.