Textbook Problem

In Problems 1-4, approximate the area under each curve over the specified interval by using the indicated number of subintervals (or rectangles) and evaluating the function at the right-hand endpoints of the subintervals. (See Example 1.)

$f\left(x\right)=x^2+x+1\text{ from }x=-1\text{ to }x=1;4$ subintervals