Question

If A=B prove AUB=AnB

Answer 1

let us take 2 sets
a={1,2,3}
b = {1,2,3}

look as union has all elements of both sets so,
a u b ={1,2,3}

as intersection is common elements in the both sets so,

a n b ={1,2,3}

Answer 2

hence of a=b then
a u b =a n b

hence proved :P
you got it @xhejni :P

Answer 3

if two sets are same let a and b
then we can say
a= b

according to definition of intersection it is function that contains common enements from both sets
as a=b so all elemnts are common
so a= a n b
or b = a n b

in union the function has all elements of both sets and in set no element repeats so

a u b = a
or
a u b = b

as a u b = a or b
and a n b = a or b
so we can conclude here that

a u b = a n b
as
a = b // defined above

Answer 4

@xhejni now :P