If the function f: R R be given by be given by find fog and gof and hence find fog (2) and gof ( −3).
Discuss the commutativity and associativity of binary operation '*' defined on A = Q − {1} by the rule a * b = a − b + ab for all, a, b ∊ A. Also find the identity element of * in A and hence find the invertible elements of A.
Given, * is a binary operation on Q − {1} defined by a*b=a−b+ab
Commutativity:
For any a, b∈A,
we have a*b=a−b+ab and b*a=b−a+ba
Since, a−b+ab≠b−a+ab
∴a*b≠b*a
So, * is not commutative on A.
Associativity:
Let a, b, c∈A(a*b)*c=(a−b+ab)*c
⇒(a*b)*c=(a−b+ab)−c+(a−b+ab)c
⇒(a*b)*c=a−b+ab−c+ac−bc+abc
a*(b*c)=a*(b−c+bc)
⇒a*(b*c)=a−(b−c+bc)+a(b−c+bc)
⇒a*(b*c)=a−b+c−bc+ab−ac+abc
⇒(a*b)*c≠a*(b*c)
So, * is not associative on A.
Identity Element
Let e be the identity element in A, then
a*e=a=e*a ∀a∈Q−{1}
⇒a−e+ae=a
⇒(a−1)e=0
⇒e=0 (As a≠1)
So, 0 is the identity element in A.
Inverse of an Element
Let a be an arbitrary element of A and b be the inverse of a. Then,
a*b=e=b*a
⇒a*b=e
⇒a−b+ab=0 [∵e=0]
⇒a=b(1−a)
⇒b=a/1−a
Since b∈Q−1
So, every element of A is invertible.
Consider f : R+ → [−5, ∞), given by f(x) = 9x2 + 6x − 5. Show that f is invertible with f−1(y).
Hence Find
(i) f−1(10)
(ii) y if f−1(y)=43,
where R+ is the set of all non-negative real numbers.
If a*b denotes the larger of 'a' and 'b' and if a o b = (a*b) + 3, then write the value of (5) o (10), where and o are binary operations.
Let A = { x ∈ Z: 0 ≤ x≤ 12} show that R = {(a,b):a,b ∈ A, |a-b|} is divisible by 4} is an equivalence relation. Find the set of all elements related to 1. Also, write the equivalence class [2].
Show that the function f: R → R defined by si neither one- one nor onto. Also, if g: R → R is defined as g(x) = 2x -1 find fog (x)
(i) Is the binary operation *, defined on set N, given by a * b = for all a,b N, commutative?
(ii) Is the above binary operation * associative?
If the binary operation * on the set of integers Z, is defined by a * b = a + 3b2 , then find the value of 2 * 4.