math
posted by Liz on .
Find the coefficient of x³ in the expansion of (2x+5)^6

From your last question:
a^6 + 6 a^5 b + 15 a^4 b^2 + 20 a^3 b^3 + 15 a^2 b^4 + 6 a b^5 + b^6
Here a = 2x
and
b = 5
so if you are looking for the x^3 term, it is found in the middle
or
20 a^3 b^3
or
20 * (2x)^3 * 5^3
= 20 * 8 * 125 x^3
=20,000 x^3