Помогите пж 2 задание

Question

Помогите пж 2 задание

---

Answer 1

3C(2n)(2n-3)/(2(2n-1)=


3*(2n)!/(2n-2n+3)*(2n-3)!/(2(2n-1))=

(2n)!/(2n-3)!*1/(2(2n-1)=

(2n*(2n-1)(2n-2)/(2(2n-1))=n(2n-2)