Consider the sets A = \(x, y) R R : x2 + y2 = 25 \, B = \(x, y) R R : x2 + 9y2 = 144 \, C = \(x, y) Z Z : x2 + y2 4 \ and D = A B. The total number of one-one functions from the set D to the set C is:
- 15120
- 18290
- 17160
- 19320
Answer
(3) 17160
Solution
D: solve x2 + y2 = 25 and x2 + 9y2 = 144
Subtracting: 8y2 = 119 ⇒ y2 = 1198, x2 = 25 - 1198 = 818
⇒ x = 92 2, y = 1198 ⇒ n(D) = 4
C: integer points with x2 + y2 4
x = 0: y = 0, 1, 2 → 5 points
x = 1: y = 0, 1 → 6 points
x = 2: y = 0 → 2 points
⇒ n(C) = 13
Number of one-one functions from D to C = 13P4 = 13 12 11 10 = 17160
Answer: (3)