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x^6 in expanded (1+3x)^12
(edited 12 years ago)
Reply 1
Avatar for Hasufel
Hasufel
16
this is (3x)^6 x (12,6) - called "12 choose 6" - or (3x)^6 x [12!/6!(12-6)!]

2nd: term you`re looking for has equal powers for each part. the bimomial coefficient of this term will be:

(8 choose 1) x^(8-r) (1/x)^r

the powers must be equal, so you equate them and solve...
(edited 12 years ago)
Original post by Hasufel
this is (3x)^6 x (12,6) - called "12 choose 6" - or (3x)^6 x [12!/6!(12-6)!]

2nd: term you`re looking for has equal powers for each part. the bimomial coefficient of this term will be:

(8 choose 1) x^(8-r) (1/x)^r

the powers must be equal, so you equate them and solve...


You need to edit that to (8 choose r)
Reply 3
Avatar for 0utdoorz
0utdoorz
OP
1
Original post by Hasufel
this is (3x)^6 x (12,6) - called "12 choose 6" - or (3x)^6 x [12!/6!(12-6)!]

2nd: term you`re looking for has equal powers for each part. the bimomial coefficient of this term will be:

(8 choose 1) x^(8-r) (1/x)^r

the powers must be equal, so you equate them and solve...


for 2nd, how did you get r? what does that stand for?
Original post by 0utdoorz
for 2nd, how did you get r? what does that stand for?


r is any number between 1 and 8. but in order to have the power of x (which for the rth term is 8-2r) equal 0, r=4
(edited 12 years ago)
Reply 5
Avatar for Hasufel
Hasufel
16
of course! 8 choose r - sorry!

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