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Binomial Series C4

Stuck on exercise in textbook.

I understand how to expand the problem.

(x+1)3(2x)\frac{(x+1)^3}{(2-x)}

(x+1)3(2x)1(x+1)^3(2-x)^-1

When expanded (to fourth term) i get (1+3x+3x2+x3)(12+x4+x28+x316)(1+3x + 3x^2 + x^3)(\frac{1}{2} + \frac {x}{4} + \frac{x^2}{8} + \frac{x^3}{16})

Now i don't really understand how to combine the two expansions i've found to make one solution as the final answer.
Reply 1
(a+b+c+d)(e+f+g+h)=(ae+af+ag+ah+be+bf+bg+bh+ce+cf+cg+ch+de+df+dg+dh)
Reply 2
Pheylan
(a+b+c+d)(e+f+g+h)=(ae+af+ag+ah+be+bf+bg+bh+ce+cf+cg+ch+de+df+dg+dh)


So multiply and add the like terms together?
Reply 3
FinalFlash
Stuck on exercise in textbook.

I understand how to expand the problem.

(x+1)3(2x)\frac{(x+1)^3}{(2-x)}

(x+1)3(2x)1(x+1)^3(2-x)^-1

When expanded (to fourth term) i get (1+3x+3x2+x3)(12+x4+x28+x316)(1+3x + 3x^2 + x^3)(\frac{1}{2} + \frac {x}{4} + \frac{x^2}{8} + \frac{x^3}{16})

Now i don't really understand how to combine the two expansions i've found to make one solution as the final answer.

The expansion works for only (1+x)^n expansion ..
so initially you had to take out a 1/2 and you end up with (1x2)1(1-\frac{x}{2})^{-1} and expand..
and multiply each of them together untill get your fourth term..
Reply 4
rbnphlp
The expansion works for only (1+x)^n expansion ..
so initially you had to take out a 1/2 and you end up with (1x2)1(1-\frac{x}{2})^{-1} and expand..
and multiply each of them together untill get your fourth term..


I did that already.

Its combining the two expansions i was having trouble with.
Reply 5
FinalFlash
I did that already.

Its combining the two expansions i was having trouble with.

what is the term they re looking for ?i.e are they looking for the coefficient of x^2,x^3,x^4??
Reply 6
rbnphlp
what is the term they re looking for ?i.e are they looking for the coefficient of x^2,x^3,x^4??


They're looking for all the terms up to term 4. I've found them for both expansions and was finidng difficulty in putting them together to create one final solution.
Reply 7
FinalFlash
They're looking for all the terms up to term 4. I've found them for both expansions and was finidng difficulty in putting them together to create one final solution.

would you mind posting it here ..
all you have to do is multiply (x+1)^3 ( by the other one) and collect the like terms together.as you said above I guess
Reply 8
rbnphlp
would you mind posting it here ..


It's in the first post.
Reply 9
FinalFlash
So multiply and add the like terms together?

yeah
Reply 10
FinalFlash
It's in the first post.

edited
Reply 11
Thanks guys :smile:

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