Section 3.2
Proof and Perpendicular Lines
Flow proof – uses arrows to show the flow
of the logical argument. Each reason in a
flow proof is written below the statement it
justifies.
Theorem 3.1
If two lines intersect to form a linear pair of
congruent angles, then the lines are
perpendicular.
Lines m and n intersect
and 1   2
m n
Theorem 3.2
If two sides of two adjacent acute angles
are perpendicular, then the angles are
complementary.
1 and 2 are adjacent and
BA  BC
 1 and  2 are complementary
Theorem 3.3
If two lines are perpendicular, then they
intersect to form four right angles.
ab
 1, 2, 3, 4
are right angles
Example 1: Find the value of x.
a)
x = 90°
b)
x = 20°
c)
x = 59°
Example 2: What can you conclude about the
labeled angles?
m  1 + m  2 = 90°
HOMEWORK (Day 1)
pg. 138 – 139; 5, 6, 12, 13, 15, 16
Example 3:
Given BA ┴ BC
Prove:  1 and
 2 are complementary.
Make a flow proof!
Example 4:
Given:  1 and  2 are a linear pair.
 2 and  3 are a linear pair.
Prove: 1   3
1
3
2
Example 5:
Given: CD ┴ CE
Prove: 1 and  2 are complementary.
HOMEWORK (Day 2)
pg. 139 – 140; 17 – 19