Question

the coefficient of x^21 in the expansion of (X + x^2)20 is​

Answer 1

ANS:

²⁰C₁

Step-by-step explanation:

The second term is :

--> ²⁰c₁ (x)²⁰⁻¹ (x²)¹

--> ²⁰c₁(x)¹⁹(x)²

-->²⁰c₁(x)²¹                   [ (x)¹⁹⁺²= (x)²¹ ]

HENCE ²⁰C₁