Question

What is the coefficient of X^2Y^2 in the expansion of (x+y)^4

Answer 1

6

Explanation:

We want to expand this; (x + y)⁴

This can be written as;

(x + y)² × (x + y)²

This gives;

(x² + 2xy + y²) × (x² + 2xy + y²)

This gives;

x²(x² + 2xy + y²) + 2xy(x² + 2xy + y²) + y²(x² + 2xy + y²) = x⁴ + 2x³y + x²y² + 2x³y + 4x²y² + 2xy³ + x²y² + 2xy³ + y⁴

Simplifying gives;

x⁴ + 4x³y + 4xy³ + 6x²y² + y⁴

Thus, the coefficient of x²y² is 6