May 23, 2009

Binomial expansion question?

Question:
Find the coeffcient of the term in x^3 in the expansion of
(2+3x)^3 (5-x)^3

how would i do this? help would be great
Answer:
These are only cubics, so the quickest solution is simply to expand each term.

(2 + 3x)³ = 8 + 12x + 18x² + 27x³

(5 - x)³ = 125 - 25x + 5x² - x³

Multiplying these together will give you

(125)27x³ + 8(-x³) + (-25x) (18x²) + (12x) (5x²)

Now all you have to do is to add them up!

Category: Science