Consider the area between the graphs x + y = 16 and a + 4 = y'. This area can be computed in two different ways using integra First of all it can be computed as a sum of two integrals f(z) da + 9(x) da where a = b C : and f (IC) g(x) = Alternatively this area can be computed as a single integral [ h ( y ) dy where a = B and h(y) = Either way we find that the area is