Question

What is the coefficient of XA,A in the expansion of (x + y)8?A. 1B. 4C. 70O D. It does not exist.

Answer 1

Using Pascal triangle

Row 8 is

1 8 28 56 70 56 28 8 1

So we can proceed to expand

`x^8+8x^7y+28x^6y^2+56x^5y^3+70x^4y^4+56x^3y^5+28x^2y^6+8xy^7+y^8`

Hence, the coeeficient is 70