A-(B ⋂ C)=(A-B) ⋃ (A-C)
According to definition,
A-B={x| x ∈A and x∉B}
A-C={x |x ∈A and x∉ C}
then
(A-B) ⋃ (A-C)={x|x∈A and x∉(B and C)
Let X=A and Y=(B ⋂ C)
then
X-Y={x | x∈X and x∉Y}
x∉Y
x∉(B ⋂ C)
x∉(B and C)
A-(B ⋂ C) or X-Y = {x|x∈A and x∉(B and C)
Therefore,
A-(B ⋂ C)=(A-B)⋃(A-C)
Hence the proof