Approximate the area under each curve by evaluating the function at the left-hand endpoints of the subintervals.

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 x=1 to x=3; 4 subintervals

4. f (x)=x2+x+1 from x=-1 to x=1; 4 subintervals