Question

What is the 8th term of the binomial expansion (x + y)10?

Answer 1

We can use the Pascal's Triangle to solve this problem. This pascal's triangle is shown in the figure below. To build the triangle, begin with the number 1 at the top, then continue placing numbers below it in a triangular pattern. In this way, each number are the numbers directly above added together. So, the expression:

$(x+y)^{10}$

Can be extended as follows, for n = 10:

$(x+y)^{10}=x^{10}+10x^{9}y+45x^{8}y^2+120x^{7}y^3+210x^{6}y^4+252x^{5}y^5+210x^{4}y^6+120x^{3}y^7+45x^{2}y^8+10xy^9+y^{10}$

So, the 8th term of the binomial expansion is:

$120x^{3}y^7$