Area of region lying inside r(t) = sin(2t) and r(t) = cos(2t)

Dear all,

I am having trouble with the following exercise and would like to ask if the step underlined in red could be please explained.

I understand everything up to that point but don't understand why only is considered in the integral. What about ?

Also, what does the mean? Does it represent the fact that the wedge (highlighted in light green below in my graph) is multiplied by 16 times?

Thank you very much.

---

Question: Find the area of the region that lies inside both and .

**Given solution: http://img830.imageshack.us/img830/9516/is2js10431.jpg**

My graph: http://img838.imageshack.us/img838/4710/isjs10431.jpg