The area (in square units) of the region enclosed by the ellipse x2 + 3y2 = 18 in the first quadrant below the line y = x is
- 3 + 1
- 3
- 3 - 34
- 3 + 34
Answer
(2) 3
Solution
Ellipse: x218 + y26 = 1; with y = x: 4x2 = 18 x = 3 2
[figure]
The shaded region = triangle under y = x (from 0 to 3 2) + part under the ellipse (from 3 2 to 3 2):
Area = 03/ 2 x dx + 1 3 3/ 23 2 18 - x2 dx
= 94 + 1 3 [ x2 18 - x2 + 9 -1 x3 2 ]3/ 23 2
= 94 + 1 3 [ 9 2 - ( 9 34 + 3 2 ) ]
= 94 + 3 - 94 = 3
Answer: (2)