Let $f$ and $g$ be continuous function on $a \leq x \leq b$ and set $p(x)=\max \{f(x), g(x)\}$ and $q(x)=\min \{f(x), g(x)\}$,
then the area bounded by the curves $y=p(x), y=q(x)$
and the ordinates $x=a$ and $x=b$ is given by
(a) $\int_{4}^{b}|f(x)-g(x)| d x$
(b) $\int_{a}^{b}|p(x)-q(x)| d x$
(c) $\left.\int_{a}^{b} \mid f(x)-g(x)\right\} d x$
(d) $\int_{a}^{b}\{p(x)-q(x)\} d x$