How to find the difference of two sets?
If A and B are two
sets, then their difference is given by A  B or B  A.
• If A = {2, 3, 4} and B = {4, 5, 6}
A  B means elements of A which are not the
elements of B.
i.e., in the above example A  B = {2, 3}
In general, B  A = {x : x ∈ B, and x ∉ A}
• If A and B are disjoint sets, then
A – B = A and B – A = B
Solved examples to find the difference of two sets:
1. A = {1, 2, 3} and B = {4, 5, 6}.
Find the difference between the two sets:
(i) A and B
(ii) B and A
Solution:
The two sets are disjoint as they do not have any elements in common.
(i) A  B = {1, 2, 3} = A
(ii) B  A = {4, 5, 6} = B
2. Let A = {a, b, c, d, e, f} and B = {b, d, f, g}.
Find the difference between the two sets:
(i) A and B
(ii) B and A
Solution:
(i) A  B = {a, c, e}
Therefore,
the elements a, c, e belong to A but not to B
(ii) B  A = {g)
Therefore, the element g belongs to B but not A.
3. Given three sets P, Q and R such that:
P = {x : x is a natural number between 10 and 16},
Q = {y : y is a even number between 8 and 20} and
R = {7, 9, 11, 14, 18, 20}
(i) Find the difference of two sets P and Q
(ii) Find Q  R
(iii) Find R  P
(iv) Find Q – P
Solution:
According to the given statements:
P = {11, 12, 13, 14, 15}
Q = {10, 12, 14, 16, 18}
R = {7, 9, 11, 14, 18, 20}
(i) P – Q = {Those elements of set P which are not in set Q}
= {11, 13, 15}
(ii) Q – R = {Those elements of set Q not belonging to set R}
= {10, 12, 16}
(iii) R – P = {Those elements of set R which are not in set P}
= {7, 9, 18, 20}
(iv) Q – P = {Those elements of set Q not belonging to set P}
= {10, 16, 18}
● Set Theory
● Sets
● Subset
8th Grade Math Practice
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