Figure Reflection Theorem  If a figure is determined by certain points, then its reflection image is the corresponding figure determined by the reflection images of those points 
Perpendicular Bisector Theorem  If a point is on the perpendicular bisector of a segment, then it is equidistant from the endpoints of the segment

Segment Congruence Theorem  Two segments are congruent if and only if they have the same length. 
Betweeness Theorem  If B is between A and C, then AB+BC=AC

Angle Congruence Theorem  Two angles are congruent if and only if they have equal measures 
CPCF Theorem i.e. Congruent Parts of Congruent Figures are congruent  If two figures are congruent, then any pair of corresponding parts is congruent 
SSS Congruence Theorem  If three sides of one triangle are congruent to three sides of the other, then the triangles are congruent

SAS Congruence Theorem  If, two sides and the included angle of one triangle, are congruent to two sides and the included angle of the other, then the triangles are congruent

ASA Congruence Theorem  If, two angles and the included side of one triangle, are congruent to two sides and the included angle of the other, then the triangles are congruent 
AAS Congruence Theorem  If, two angles and a nonincluded side of one triangle, are congruent respectively to two angles and a nonincluded side of the other then the two triangles are congruent

HypLeg Congruence Theorem  If, the hypotenuse and leg of one triangle are congruent to the hypotenuse and leg of the other, then the two triangles are congruent 
SSA Congruence Theorem  If, two sides and the angle opposite the longer of the two sides in one triangle are congruent respectively to two sides and the angle opposite the longer of the two sides in the other, then the two triangles are congruent. 
Right Triangle Altitude Theorem  In a right triangle The altitude to the hypotenuse is the geometric mean of the segments into which it divides the hypotenuse.
Each leg is the geometric mean of the hypotenuse and the segment of the hypotenuse adjacent to the leg.

Properties of a Parallelogram Theorem  In any parallelogram each diagonal forms two congruent triangles, opposite sides are congruent, and the diagonals intersect at their midpoints

SAS Inequality Theorem  If two sides of a triangle are congruent to two sides of a second triangle, and the measure of the included angle of the first triangle is less than the measure of the included angle of the second, then the third side of the first triangle is shorter than the third side of the second 
Figure Size Change Theorem  If a figure is defined by certain points, then its changed size image is the corresponding figure determined by the size change images of those points. Notice the properties. 
Extremes Property  If a/b = c/d, then ad = bc

Exchange Property
 If a/b = c/d, then a/c = b/d

Reciprocal Property  If a/b = c/d, then b/a = d/c 
Similar Figures Theorem  If two figures are similar, then corresponding angles are congruent and corresponding lengths are proportional 
Fundamental Theorem of Similarity  If P ~ P' and r is the ratio of similitude, then:
Perimeter (P') = r times Perimeter (P)
Area (P') = r(sq) times Area(P)
Volume (P') = r(cu) times Volume (P) 
SSS Similarity Theorem  If the three sides of one triangle are proportional to three sides of a second triangle, then the triangles are similar. 
AA Similarity Theorem  If two triangles have two angles of one congruent to two angles of the other, then the triangles are similar. 
SAS Similarity Theorem  In two triangles, if the ratios of two pairs of corresponding sides are equal and the included angles are congruent, then the triangles are similar. 
SideSplitting Theorem  If a line intersects ray OP and ray OQ in distinct points X
and Y such that OX/XP = OY/YQ, then line XY
is parallel to line PQ. 
RadiusTangent Theorem  A line is tangent to a circle; if and only if it is perpendicular to the radius at endpoint of the radius of circle. 
Exterior Angle Theorem  In a triangle, the measure of an exterior angle is equal to the sum of the measures of the two non adjacent interior angles.

Exterior Angle Inequality  In a triangle, the measure of an exterior angle is equal to the sum of the measures of the two nonadjacent interior angles. 
Unequal Sides Theorem  If two sides of a triangle are not congruent, then the angles opposite to them are not congruent, and the largest angle is opposite the longer side. 
Unequal Angles Theorem  If two angles of a triangle are not congruent, then the sides opposite to them are not congruent, and the longer side is opposite the larger angle 
Isosceles Right Triangle Theorem  In an isosceles right triangle, if a leg is x then the hypotenuse is x
times the 2. 
306090 Triangle Theorem  In a 306090 right triangle, if the short leg is x then the longer leg
is x times 3 and the hypotenuse is 2x. 
Isoperimetric Theorem  Of all solids with the same volume, the sphere has the least surface area. 
Isoperimetric Theorem  Of all solids with the same surface area, the sphere has the max volume 
Isoperimetric Theorem  Of all plane figures with the same area, circle has the least perimeter 
Isoperimetric Inequality  If a plane figure has area A and perimeter P, then A
is greater then or equal to P2/4. 
Tangent Square Theorem  The power of point P for circle O is square of the length of a segment tangent to circle O. 
Secant Length Theorem  Suppose one secant intersects a circle at A and B, and a second
secant intersects the circle at C and D. If the secants intersect
at P, then AP times BP equals CP times DP. 
TangentSegment Theorem  The measure of an angle between two tangents, or between a tangent and a secant, is half the distance of the intercepted arcs 
TangentChord Theorem  The measure of an angle formed by a tangent and a chord measures half of the measures of intercepted arc. 
AngleSecant Theorem  The measure of an angle formed by two secants intersecting outside a circle is half the difference of the arcs intercepted by it. 
AngleChord Theorem  The measure of an angle formed by two intersecting chords is onehalf the sum of the measures of the arcs intercepted by it and its vertical angle. 
Inscribed Angle Theorem  In a circle the measure of an inscribed angle is onehalf the measure of its intercepted arc. 
ArcChord Congruence Theorem  In a circle or in congruent circles:
(1) If two arcs have the same measure, they are congruent and their chords are congruent
(2) If two chords have the same length, their minor arcs have the same measure. 
ChordCenter Theorem  (1) The line containing the center of a circle perpendicular to a chord bisects the chord.
(2) The line containing the center of a circle and the midpoint of a chord bisects the central angle determined by the chord.
(3) The bisector of the central angle of a chord is perpendicular to the chord and bisects the chord.
(4) The perpendicular bisector of a chord of a circle contains the center of the circle 
Vector Addition Theorem  The sum of the vectors (a,b) and (c,d) is the vector (a
+ c, b + d). Notice the following properties:
A.Vector addition is commutative.
B.Vector addition is associative
C.(0,0) is an identity for vector addition
D.Every vector (a,b) has an additive inverse (a,b) 