Theory | Reference Notes | Elementary Group Theory | Subject: Mathematics Grade XII

1. Algebraic Structures: An algebraic structure of a set G under an operation on G and denoted by (G, ) satisfy the following properties.

• Closed = if a, b ∊ G ⇒ a * b ∊ G
• Commutative = if a * b = b * a, for each a, b ∊ G
• Associative = if (a * b) * c = a * (b * c), for each a, b, c ∊ G
• Identity = if a * e = e * a, for e ∊ G
• Inverse = if a * b = e = b * a ⇒ b is inverse of a

2. Group: An algebraic structure (G, ), where G is a non-empty set with an operation ‘ ’ defined on it, is said to be group, if the operation satisfies the following axioms (called group axioms).

• Closure Axiom → a * b ∊ G for all a, b ∊ G
• Associative Axiom → (a * b) * c = a * (b * c) for all a, b, c ∊ G
• Identity Axiom → a * e = e * a, for e, a ∊ G
• Inverse Axiom → a * b = e = b * a, where a and b ∊ G, b is the inverse of a

3. Congruent Modulo m: If a positive integer a is divided by a positive integer m giving the positive integers k and b (<m) as the quotient and the remainder respectively then we call ‘a congruent b modulo m’ and I written as a = b (mod. m).

Cayley’s table