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# maths binomial expansion help watch

1. find the coefficient of the term in x^3 in the expansion of (2+3x)^3 (5-x)^3
i have expanded both of them and got
(8+36x+54x^2+27X^3) and(125-75x+15x^2-x^3)

i don't know what to do next help
2. (Original post by yeah1106)
find the coefficient of the term in x^3 in the expansion of (2+3x)^3 (5-x)^3
i have expanded both of them and got
(8+36x+54x^2+27X^3) and(125-75x+15x^2-x^3)

i don't know what to do next help
Well.. you've expanded (2+3x)^3 and (5-x)^3 and you're looking for the coefficient of x^3 in (2+3x)^3(5-x)^3.. so what can you do with the two expansions?
3. (Original post by SeanFM)
Well.. you've expanded (2+3x)^3 and (5-x)^3 and you're looking for the coefficient of x^3 in (2+3x)^3(5-x)^3.. so what can you do with the two expansions?
do you times it together
4. (Original post by yeah1106)
do you times it together
Correct

If you are confident, you can save some time by only multiplying things that will get you a coefficient of x^3.
5. how to know which will give you coefficient of x^3
6. awwww 4 mins too late ;(

(Original post by SeanFM)
Well.. you've expanded (2+3x)^3 and (5-x)^3 and you're looking for the coefficient of x^3 in (2+3x)^3(5-x)^3.. so what can you do with the two expansions?

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