Area of region example

Find area of region bounded by parabola x = y2 and the line y = x.

Graph:

PIC

We’ll let y go from 0 to 1. Then x goes from y2 to y.

Area is

01 y2ydxdy = 01(      )
 x |x=y
   x=y2dy
= 01(y - y2)dy
= [y2-
2 -y3-
3]01
= 1
--
2 -1
--
3 = 1
--
6

Note: if asked to integrate a function f(x,y) over that region, you’d need to compute

01 y2yf(x,y)dxdy.