Difference between revisions of "Contrapositive"
(→See also) |
|||
| (3 intermediate revisions by 3 users not shown) | |||
| Line 3: | Line 3: | ||
A [[conditional]] statement is usually expressed as | A [[conditional]] statement is usually expressed as | ||
| − | If '''P''', then '''Q''' | + | If '''P''', then '''Q'''. |
The contrapositive statement is usually expressed as | The contrapositive statement is usually expressed as | ||
| − | If not '''Q''', then not '''P''' | + | If not '''Q''', then not '''P'''. |
where '''P''' denotes a condition and '''Q''' denotes another condition. | where '''P''' denotes a condition and '''Q''' denotes another condition. | ||
| Line 14: | Line 14: | ||
Given the conditional statement "If a polygon has 3 sides, then it is a triangle", the contrapositive is "If a polygon is not a triangle, then it does not have 3 sides". | Given the conditional statement "If a polygon has 3 sides, then it is a triangle", the contrapositive is "If a polygon is not a triangle, then it does not have 3 sides". | ||
| + | |||
| + | == See also == | ||
| + | * [[Logic]] | ||
Revision as of 13:08, 19 December 2016
A contrapositive of a statement is always true, assuming that the conditional statement is true. However, if the conditional statement is false, then the contrapositive is also false.
A conditional statement is usually expressed as
If P, then Q.
The contrapositive statement is usually expressed as
If not Q, then not P.
where P denotes a condition and Q denotes another condition.
Examples
Given the conditional statement "If a polygon has 3 sides, then it is a triangle", the contrapositive is "If a polygon is not a triangle, then it does not have 3 sides".
