Q. The sum of cubes of the first ' $n$ ' natural numbers $=$ $\left(\frac{n(n+1)}{2}\right)^2\left[\right.$ i.e. $\left.1^3+2^3+3^3+\ldots+n^3=\left[\frac{n(n+1)}{2}\right]^2\right]$. Using this result find the value of $11^3+12^3+13^3+\ldots$ $+20^3$.
Squares and Square Roots and Cubes and Cube Roots
Solution: