Let A = \-2, -1, 0, 1, 2, 3, 4\. Let R be a relation on A defined by xRy if and only if 2x + y 2. Let l be the number of elements in R. Let m and n be the minimum number of elements required to be added in R to make it reflexive and symmetric relations respectively. Then l + m + n is equal to :
- 34
- 32
- 33
- 35
Answer
(3) 33
Solution
(x, y) R y 2 - 2x:
x = -2: y 6 → all 7 values
x = -1: y 4 → 7 values
x = 0: y 2 → -2, -1, 0, 1, 2 (5 values)
x = 1: y 0 → -2, -1, 0 (3 values)
x = 2: y -2 → -2 (1 value)
x = 3, 4: none
l = 7 + 7 + 5 + 3 + 1 = 23
Reflexive: (x, x) R 3x 2 x 0.
Missing: (1, 1), (2, 2), (3, 3), (4, 4) m = 4
Symmetric: pairs (x, y) R with (y, x) R:
(-2, 3), (-2, 4), (-1, 2), (-1, 3), (-1, 4), (0, 2)
(e.g. (3, -2): 6 - 2 = 4 > 2)
n = 6
l + m + n = 23 + 4 + 6 = 33
Answer: (3)