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f is homomorphism and if H is subgroup then f(H) is subgroup

f(g^n)=(f(g))^n for all n in Z

homomorphism carries identity on identity

Kernel is subgroup

If f(g) = g' then f^-1(g')= {xE G | f(x)=g'}= gKer f.

let f be homomorphism and if order of g=n then order of f(g) divides n

Kernel of homomorphism, definition and example

definition of homomorphism

G/Z theorem let Z(G) be the center of G. If G/Z(G) is cyclic, then G is Abelian.

Normal Subgroup Test A subgroup H of G is normal in G iff xHx'1 contained in H for all x in G.

Let G be a group and let Z(G) be the center of G. If G/Z(G) is cyclic, then G is Abelian.

Fermat’s Little Theorem in detail

Factor group definition

A subgroup H of a group G is called a normal subgroup of G if aH=Ha for all a in G.

Fermat’s Little Theorem

Corollary Let G be a finite group, and let a belongs to G. Then, a|G|= e.

Corollary -A group of prime order is cyclic.

Corollary |a| Divides |G|, the order of each element of the group divides the order of the group.

converse of Langranges theorem not true

Langranges Theorem-If G is a finite group and H is a subgroup of G, then |H| divides |G|

aH is a subgroup of G if and only if a belong to H

aH = Ha if and only if H = aH inverse(a)

number of elements in two left cosets are equal

aH=bH iff inverse(a)b belongs to H