When straight lines intersect, the two angles next to each other are called
adjacent angles.They share a vertex, a side, and no interior points. Adjacent
angles along a straight line are always supplementary.
When straight lines intersect, opposite angles, or angles nonadjacent to
each other, are called vertical angles. They are always congruent or equal
in measure. The symbol for congruent is.
When two lines intersect and form four right angles, the lines are con-
sidered perpendicular.
Three-Lined Intersections
A transversal lineintersects two or more lines, each at a different point.
Because a transversal line crosses at least two other lines, eight or more
angles are created. When a transversal intersects a pair of parallel lines, cer-
tain angles are always congruent or supplementary. Pairs of these angles
have special names:
(^12)
3 4
∠ 1 ∠ 2 ∠ 3 ∠ 4
m1 = m2 = m3 = m4 = 90 ̊
1
2
3
4
∠ 1 ∠3, m1 = m 3
∠ 2 ∠4, m2 = m 4
a
b
1
2
3
4
m∠1 + m∠2 = 180 ̊
m∠2 + m∠3 = 180 ̊
m∠3 + m∠4 = 180 ̊
m∠4 + m∠1 = 180 ̊
m∠1 + m∠2 + m∠3 + m∠4 = 360 ̊
501 Geometry Questions