Sum both sides of the identity $k^{2}-(k-1)^{2} = 2k-1$ from $k=1$ to $k=n$ and use question $35$ to find
- a formula for $\displaystyle{}\sum_{k = 1}^{n}(2k − 1)$ (the sum of the first $n$ odd natural numbers).
- a formula for $\displaystyle{}\sum_{k = 1}^{n} k.$