Just turn to Cylindrical Coordinate, please don't concern about rectangular coordinate

I am confused that, Why "?" range is from 0 to pi/2? Why "?"couldn't from 0 to pi?

9. (40 points) Integrate the function F(x, y, z) = xy using rectangular coordinates and then using cylindrical coordinates over the region (volume) given below. Use rectangular below and cylindrical coordinates on the following page. E: { ( x , y , z ) 1 0 S x 5 2, 0 S y S v 4 - x2, 0 Szs6-y)b. Using cylindrical coordinates. Xy - PLANIT Os y