Exercise 4. Consider a monotonically strictly increasing function (i.e-a function $f(x)$ whose graph is going up, that is, if $x<y$ then $f(x)<f(y)$.) Let $a<b$. Order the following three quanities in increasing magnitude: $\int_{a}^{b} f(x) d x$, $R_{100}, L_{100}$ and explain your reasoning geometrically.