# Lecture - 9 Chapter 9 Sequences & Series

Introduction to Special Series,

Sum of first *n* natural numbers

1+2+3+…+n=\frac{n(n+1)}{2}

Inspirational Story of Mathematician Gauss when he was in elementary school told by Prof. Arvind Gupta

Sum of Squares of first *n* natural numbers

1^2+2^2+3^2+…+n^2=\frac{n(n+1)(2n+1)}{6}

Sum of Cubes of first *n* natural numbers

1^3+2^3+3^3+…+n^3= \left ( \frac{n(n+1)}{2} \right )^2