9Th Grade Geometry Theorems

Front 1

Midpoint Thm

Back 1

If M is the midpoint of segment AB, then
2AM=AB and AM=1/2AB
2MB=AB and MB=1/2AB

Front 2

Angle bisector thm

Back 2

If ray BX is the bisector of ∠ABC, then
2m∠ABX=m∠ABC; m∠ABX=1/2m∠ABC
2m∠XBC=m∠ABC; m∠XBC=1/2m∠ABC

Front 3

Vertical Angle thm

Back 3

vertical ∠'s are congruent

Front 4

Vertical Angle thm
conjecture

Back 4

If angles are vertical, then they are congruent.

Front 5

If two lines are perpendicular,

Back 5

then adjacent ∠'s are congruent.

Front 6

If two lines form congruent adjacent ∠'s,

Back 6

then the lines are perpendicular

Front 7

If the exterior sides of two adjacent acute ∠'s are perpendicular,

Back 7

then the ∠'s are complementary.

Front 8

Congruent Supplement thm

Back 8

If 2 ∠'s are supplements of congruent ∠'s (or the same ∠), then the 2 ∠'s are congruent.

Front 9

Congruent complement thm

Back 9

If 2 ∠'s are complements of congruent ∠'s (or the same ∠), then the 2 ∠'s are congruent.

Front 10

If 2 parallel planes are cut by a third plane,

Back 10

then the lines of intersection are ||.