Need to Know
Sets
The rules you must have ready for the exam.
How to use this: say each rule in your head, then tap Show me to check.
Notation
1 ruleRule 01
The symbols
- ∩ intersection — in both
- ∪ union — in either
- A′ complement — outside
- A\B difference — in A not B
- #A how many · ∅ null set
Listing elements
1 ruleRule 02
Method
Work out each bracket as its own set first, then combine with ∩ or ∪.
Venn diagrams
1 ruleRule 03
Two sets
Four regions: only P, the overlap (both), only Q, and outside both (inside U).
(P∪Q)′ = outside both circles.
Numbers in regions
1 ruleRule 04
Solve for the overlap
Put an expression in each region; they add up to #U. Solve for the unknown (usually the overlap).
Mathslive.ie · Sets · Need to Know