1. If AB ∥ BC, then Collinear(A,B,C).
2.
For two angle ∠[l1,l2], ∠[l3,l4]. If l1 = l3 and l2 ∥ l4, then ∠[l1,l2] = ∠[l3,l4].
For example, in parallelogram ABCD, AD ∥ BC and AC = CA, hence ∠[CAD] = ∠[ACB].
3. if AB ∥ CD and E is the intersection of AC and BD, then EA / EC = EB / ED.
4. If AB ∥ CD and CD ⊥ EF, then AB ⊥ EF.
5. If AB ⊥ CD, then ∠[AB,CD] = [1] ( or 90 degrees).
6. In right riangle ACB, ∠C = [1], if midpoint(E, A B), then Circumcenter (E,A B C) and EA = EB = EC.
7. If AB ⊥ CD and CD ⊥ EF, then AB ∥ EF.
8. For four points A,B,C,D, if AC ⊥ BC and AD ⊥ BD, then Cyclic(A,B,C,D).
9. For a circle c(O,AB) and a point C on Circle c, if Collinear(A,B,O), then AC ⊥ BC and ∠ACB = [1].
10. If AB is the Diameter of a circle and point C is on the circle, then AC ⊥ BC,
11. Angle of circumference equals to half of angle of center,
12. If AB ∥ CD and Cyclic(A,B,C,D), then ∠ABC = ∠DAB.
13. If Cyclic(A,B,C,D), then ∠ADB = ∠ACB and vice verse.
14. Chord tangent angle ,
15.
Line passing the centers of two circles is perpendicular to the common chord of two circles. ,
For example, two circles C1(O,AB) and C2(O1,AB), AB are two common points, then OO1 ⊥ AB.
16.
The Addition for Full Angle.
If ∠[l1,l2] = ∠[l3,l4] and ∠[l5,l6] = ∠[l7,l8], and l2 = l6 and l4 = l7, then ∠[l1,l4] = ∠[l5,l8] ,
17.
ASPP12.
If ∠[l1,l2] = ∠[l3,l4] and l1 ∥ l2, then l3 ∥ l4.
Because if l1 ∥ l2, ∠[l1,l2] = [0]. Hence ∠[l3,l4] = [0].
18.
ASPP13,
If ∠[l1,l2] = ∠[l3,l4] and l1 ∥ l3, then l2 ∥ l4.
19.
ASTT12,
If ∠[l1,l2] = ∠[l3,l4] and l1 ⊥ l2, then l3 ⊥ l4.
20.
ASTT13,
If ∠[l1,l2] = ∠[l3,l4] and l1 ⊥ l3, then l2 ⊥ l4.
21. Special Angles,
22. Supplementary Angle,
23. Isoceless Triangle.
24 Isoceless Triangle Theorem.
For a isoceless triangle ABC and a point D on line BC, if any one of following statement is true, the other two are also true .
1. AD ⊥ BC, 2. D is the midpoint of BC, 3. ∠BAD = ∠DAC,
25.
Congruent Triangle. ,
Triangles are called congruent if they have the same size and shape. That is, corresponding angles have the same measure, and corresponding sides have the same length.
26 #ASA,
ASA (angle-side-angle) congruence: ,
Two triangles are congruent if a pair of corresponding angles and the included side are equal. ,
27 #SAS,
SAS(side-angle-side) congruence,
Two triangles are congruent if a pair of corresponding sides and the included angle are equal.
28 #SSS,
SSS (side-side-side) congruence,
Two triangles are congruent if their corresponding sides are equal.
29 #SAS,
SAS (side-angle-side) congruence for right triangles.
Two right triangle are congruent if their two corresponding cartesian edges are equal. ,
30.
Similar triangles,
Similar triangles are triangles that have the same shape but possibly different size. In particular, corresponding angles are congruent, and corresponding sides are in proportion.
31 #AAA,
AAA (angle-angle-angle) similarity,
If two triangles have two corresponding angles that are congruent, then the triangles are similar. Because the sum of the angles in a triangle must be PI, we really only need to know that two pairs of corresponding angles are congruent to know the triangles are similar.
32 #SAS,
SAS (side-angle-side) similarity,
The side-angle-side (SAS) similarity test says that if two triangles have two pairs of sides that are proportional and the included angles are congruent, then the triangles are similar. ,
33 #SSS,
SSS (side-side-side) similarity,
If two triangles have all three pairs of sides in proportion, the triangles are similar.
34. Ratio by similarity,
35.
Middle Connection Theorem for Triangles,
The line connect the midpoints of two sides of triangle is parallel to the third side of the triangle.
36.
The hypotenuse of a right triangle is the diameter of the circumscribed circle of the triangle, and the midpoint of the hypotenuse is the center of the circle.
For a right triangle ACB, if AC ⊥ BC and D is the midpoint of AB, then DC = DA = DB, D is the center of circle ABC.
37.
Equalateral Triangles,
An equilateral triangle is a triangle in which all three sides have equal lengths.
38.
Pythagorean Theorem,
In any right triangle, the area of the square whose side is the hypotenuse (the side of a right triangle opposite the right angle) is equal to the sum of areas of the squares whose sides are the two legs (i.e. the two sides other than the hypotenuse). ,
39. The sum of three interior angles of a triangle is [0]. (or 180 degree for traditional angle).
40.
Parallelogram ,
A parallelogram is a quadrilateral with two sets of opposite parallel sides.
41. Middle Connection Theorem for Trapzoid.
42.
Ratio ,
Use Ratio in Deductive Database Method.
43.
Ratio by angle bisector,
In triangle ABC, if AD is the bisector of angle A, and D is on line BC, then AB/BD = AC/DC.
1. The Definition of Full Angle.
A full angle is defined as an ordered pair of two lines u and v denoted by ∠[u,v].
2. ∠[u,v] = - ∠[v,u].
3. ∠[u,v] = ∠[0] if and only if u ∥ v (including u = v).
4. ∠[u,v] = ∠[1] if and only if u ⊥ v.
5 # Addition of Full Angle.
∠[u,s] + ∠[s,v] = ∠[u,v]. This rule to split an angle into two or more angles.
For example, for any line m, we have ∠[u,v] = ∠[u,m] + ∠[m,v],
6.
If l ⊥ v or ∠[l,v] = ∠[1], then ∠[u,v] = ∠[u,l] + ∠[l,v] = ∠[u,l] + ∠[1].
For example, if we have AC ⊥ BC, then ∠[CBA] = ∠[BAC] + ∠[1].
7.
The Isoceless Triangle Theorem for Full Angle.
If AC = BC, we have ∠[ABC] = ∠[CAB]. Conversely, if ∠[ABC] = ∠[CAB], then AB = AC or A, B and C are collinear.
8.
The Inscribed Angle Theorem.
Points A,B,C and D are cylic iff ∠[ABC] = ∠[ADC].
9. If Cyclic( A,B,M,N), then ∠[AB, AM] = ∠[BN,NM]. Hence we have ∠[AB, CD] = ∠[AB, AM] + ∠[AM, CD] = ∠[BN,NM]] + ∠[AM, CD].
10. Rule 10.
11. If AB is the diameter of the circumcircle of triangle ABC and D is on the circumcircle, then for any line FG, we have ∠[CD,FG] = ∠[DBA] + ∠[ACB] + ∠[BC, FG]].
12. If O is the intersection of Circle(O1, O P1 P3 I ) and Circle(O2, O P2 P4 J ) and Collinear(O, I, J), then ∠[P1O, OP2] = ∠[P1P2, IP3] + ∠[JP4, P2P4].
13. If O is the circumcenter of triangle ABC, then ∠[BOC] = 2 ∠[BAC].
14. For a circle(O, A B C D), if O is the intersection of AD and BC, then ∠[AOB] = 2 ∠[CDA].
15. For a circle(O, A B), O is the center of circle, we have ∠[OAB] = ∠[ABO]. ,
16.
If triangle ABE is a right triangle and O is the midpoint of the hypotenuse(i.e. AB), then for any line CD, we have,
∠[AB, CD] = ∠[BAE] + ∠[1] + ∠[BE, CD] ,
17. For a circle(O, ABC) and D is midpoint of BC, we have ∠[AB, EF] = ∠[BOD] + ∠[AC,EF]. ,
18. For a circle(O,ABF) and E is the midpoint of AF, we have ∠[AB, CD] = ∠[EOA] + ∠[BF, CD].
19. If G is the orthocenter of A, B, C, ∠[AE, HI] = ∠[AE, BE] + ∠[BE, HI] = ∠[1] + ∠[BE, HI],
20. If A is the incenter of P2, K, I, ∠[AB, CD] = ∠[AB, BK] + ∠[BK, CD] = ∠[1] + ∠[KI, KA] + ∠[IA, IK] + ∠[BK, CD].
21. Equal Angle found in Geometry Deductive Database.
22. If AB ⊥ AC and AB = AC, then ∠[AB,AC] = 2 ∠[AB,BC].
23. If AB ⊥ AC and AB = AC, then 2 ∠[AB,DE] = 2 ∠[AB,BC] + 2 ∠[BC,DE] = ∠[1] +2 ∠[BC,DE].
24. If OB // DE and A is on Circle(O,B), then 2 ∠[AB, DE] = ∠[OA,OB],
25. A is on Circle(O,B), then 2 ∠[AB, DE] = ∠[OA,OB] + 2 ∠[OA,DE],
26. CD is the diameter of Circle(A, BCD), AB ⊥ CD, then 2 ∠[DB,BA] = ∠[0].
27. A, B, C, D, E are cyclic and AC = AB, then 2∠[AB, BC] = ∠[CE, ED].
28. If A, B, E, F, G are cyclic and AE = AF, then 2 ∠[AB, CD] = 2 ∠[BE, CD] + ∠[EG, GF].
29. If AB = AC = BC, i.e. triangle ABC is an equilateral triangle, then 3 ∠[AB, BC] = ∠[0]. ,
JGEX Help