A function is defined over an interval [a, b].

(a) Graph indicating the area A under from a to b. 

(b) Approximate the area A by partitioning [a, b] into three subintervals of equal length and choosing u as the left endpoint of each subinterval. 

(c) Approximate the area A by partitioning [a, b] into six subintervals of equal length and choosing u as the left endpoint of each subinterval. 

(d) Express the area A as an integral. 

(e) Use a graphing utility to approximate the integral.

f(x) = x² + 3, [0, 6]