In Lecture Notes 18 on about the second page it is said:

1^2+2^2+...+n^21/3(base)(height)=1/3n^2*n

So all of this has to do with the area under x^2 so if b=10 and n=5 that means the area under x^2 is divided into 5 parts each part being 2 units wide. So for the b and n I specified what would be the actual value for (base) and the actual value for (height). This is not clear to me.

Question

In Lecture Notes 18 on about the second page it is said:

1^2+2^2+...+n^2>1/3(base)(height)=1/3n^2*n

So all of this has to do with the area under x^2 so if b=10 and n=5 that means the area under x^2 is divided into 5 parts each part being 2 units wide. So for the b and n I specified what would be the actual value for (base) and the actual value for (height). This is not clear to me.