Question

answer second one
If A={2,3,5},,.........

Answer 1

AUphi = A(b'coz any set union phi is the set itself)
and
phiUA = A
that means both r equal...

hope this helps:p

Answer 2

A={2,3,5}
i)AUθ = {2,3,5}U{ }=A-----(1)

ii) θ UA= { } U {2,3,5}= A---(2)

(1)=(2)
A U θ = θ U A = A
Here i used θ instead of null set . i don't have that symbol