Declarative Sentence:
• Two straight angles are congruent.

Conditional Form:
• If two angles are straight angles, then they are congruent.
• The clause following the word If is called the hypothesis.
• The clause following the word Then is called the conclusion.
• The conditional statement "If p, then q" can be written in symbols as p => q.

Negation- The negation of any statement p is the statement "not p"
This is written as ~p so ~~p = p

Converse, Inverse, and Contrapositive

1.A converse (If q, then p)
2.An inverse (if ~p, then ~q)
3.A contrapositive (If ~q. then ~p)

Theorem-If a conditional statement is true, then the contrapositive of the statement is also true.
(If p, then q <=> If ~q, then ~p.)

CHAINS OF REASONING

Each proof that you do involves a series of steps in a logical sequence.
In many cases, the sequence will take the following form.
q and q => r, then p => r.
This is called a chain rule and is also known as a chain of reasoning.