a) The rectangles in the graph below illustrate a ? left endpoint right endpoint midpoint Riemann sum for $\displaystyle f(x) = \frac{x^2}{12}$ on the interval $\lbrack 4, 8 \rbrack$.
The value of this Riemann sum is , and this Riemann sum is an ? overestimate of equal to underestimate of there is ambiguity the area of the region enclosed by $\displaystyle y = f(x)$, the x-axis, and the vertical lines x = 4 and x = 8.

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b) The rectangles in the graph below illustrate a ? left endpoint right endpoint midpoint Riemann sum for $\displaystyle f(x) = \frac{x^2}{12}$ on the interval $\lbrack 4, 8 \rbrack$.
The value of this Riemann sum is , and this Riemann sum is an ? overestimate of equal to underestimate of there is ambiguity the area of the region enclosed by $\displaystyle y = f(x)$, the x-axis, and the vertical lines x = 4 and x = 8.