The number of non-empty equivalence relations on the set {1,2,3} is
A. 6
B. 7
C. 5
D. 4
Explanation:
Let R be the required relation A = {(1, 1) (2, 2), (3, 3)} (i) | R | = 3, when R = A (ii) | R | = 5, e.g. R = A {(1, 2), (2, 1)} Number of R can be [3] (iii) R = {1, 2, 3} × {1, 2, 3}
2
Let ƒ : RR be a twice differentiable function such that ƒ(x + y) = ƒ(x) ƒ(y) for all x, y R. If ƒ'(0) = 4a and ƒ staisfies ƒ''(x) – 3a ƒ'(x) – ƒ(x) = 0, a > 0, then the area of the region R = {(x,y) | 0 y ƒ(ax), 0 x 2} is :