Question

What is the coefficient of x^2 y^3 in the expansion of (2x+y)^5

Answer 1

If it's x²y³ then we know it's the second term of the expansion, that known we can use the combination

C(5, 2) = 5!/(2!.3!) = 10

Then if we had something like

(a + b)^5 our second term would be 10a²b³ but as we can see it's "a²"

And in our case we have 2x as a

So we must do 2² too

2² = 4

10 . 4 = 40

Then our second term of the expansion would be

40x²y³