→ downward parabola; vertex at (0, 9); latus rectum = 1
The required area is symmetrical with respect to the y-axis, in this case, integrate the half of the area then double the result to get the total area. The use of symmetry will greatly simplify our solution most especially to curves in polar coordinates.
Using Horizontal Strip
The strip shown will start from y = 0 and end to y = 9
Using Vertical Strip