- If f(x)≥g(x) on the interval between x=a and
x=b, then the area of the region bounded by the
curves y=f(x), y=g(x), x=a and x=b is
∫ba(f(x)−g(x))dx.
- If f(x)<g(x), we instead want ∫ba(g(x)−f(x))dx. In general, we always want
∫baheight(x)dx, where the height is
the larger function value minus the smaller one. This
can also be written as ∫ba|f(x)−g(x)|dx.
- If we are not told the beginning and ending values
of x, we need to solve f(x)=g(x) to figure them
out.
- Sometimes it is easier to slice horizontally than
vertically. In that case we do the work as above, but
with larger and smaller functions of y, and we wind
up with an integral ∫dcwidth(y)dy,
where c and d are the smallest and largest values
of y.
|