Algebra and Trigonometry 10th Edition

As we can see, the sums of the first $n$ consecutive odd integers is $n^2$. $1+3+5+7+9+11=36=6^2$ $1+3+5+7+9=25=5^2$ $1+3+5+7=16=4^2$ $1+3+5=9=3^2$ $1+3=4=2^2$