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.)
1. f (x)=4x-x2 from x=0 to x=2; 2 subintervals
2. f (x)=x3 from x=0 to x=3; 3 subintervals
3. f (x)=9-x2 from x1 to x=3; 4 subintervals
4. f (x)=x2x+1 from x=-1 to x=1; 4 subintervals