Download Lesson 1.4

Lesson 1.4
Beginning Proofs
Two-column Proofs
• Much of the challenge of geometry is found in
proving things.
• Two-column proofs are the major type of proof you
will use in this class.
• You will use theorems to write two-column proofs.
A theorem is a mathematical statement that can be
proved.
Two-column proof diagram
Theorem 1
• If two angles are right angles, then they are
congruent.
• Proof:
Given: <A is a right angle.
<B is a right angle.
Prove: <A is congruent to <B.
Theorem 2
• If 2 angles are straight angles, then they are
congruent.
• Proof:
Given: <ABC is a straight angle.
<DEF is a straight angle.
Prove: <ABC is congruent to <DEF.
Example
• Given: m<RST = 50
m<TSV = 40
<X is a right angle
Prove: <RSV is congruent to <X.
Homework
• Quiz tomorrow over sections 1.1 – 1.4
• Pages 26 – 27 #3, 7, 9, 11