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Compute the area between the graphs of functions

Let

    \[ f(x) = x^{1/3}, \qquad g(x) = x^{1/2}. \]

Find the area between the graphs of f and g on the interval [0,2].


First, we draw the graph, shading the region S between the two graphs in blue.

Rendered by QuickLaTeX.com

For this exercise, since f and g cross in the interval we are interested (and we are calculating the area between the graphs, so we’re really looking at the integral of |f(x) - g(x)|) we split the integral into two pieces (at the point the functions cross).

    \[   a(S) = \int_0^2 |f(x) - g(x)| \, dx &= \int_0^1 \left(x^{1/3} - x^{1/2} \right) \, dx + \int_1^2 \left(x^{1/2} - x^{1/3}\right) \, dx \]

We’ve already computed these integral in the previous two exercises (here and here). Using the results of those exercises we then have,

    \begin{align*}    \int_0^1 \left( x^{1/3} - x^{1/2} \right) \, dx + \int_1^2 \left(x^{1/2} - x^{1/3} \right) \, dx &= \frac{1}{12} + \frac{4 \sqrt{2}}{3} - \frac{3 \sqrt[3]{2}}{2} + \frac{1}{12} \\  &= \frac{4 \sqrt{2}}{3} - \frac{3 \sqrt[3]{2}}{2} + \frac{1}{6}. \end{align*}

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