Question

plse friends, help me to solve this

Answer 1

i still think a contradication is the best setup

assume that AnB = AnC, and show that B not= C is a contradiction

let x be a general element in AnB
x in A and x in B

since AnB = AnC, then x is an element of AnC
x in A and x in C

but x in B and x in C contradicts B not= C

Answer 2

the second part should run the same sort of course

Answer 3

let x in B, x not in A

x in AuB

since AuB = AuC, then x in AuC; but since x not in A, then x in C

x in B and x in C contradicts B not= C