Proof of Pythagorean Theorem (Sim Triangles)
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Choose the correct missing statements and reasons in the questions below for the following proof.
Given right triangle ΔABC, as seen below, with altitude ¯CD, prove that AC2+BC2=AB2.

Given right triangle ΔABC, as seen below, with altitude ¯CD, prove that AC2+BC2=AB2.

Statement | Reason |
1.ΔABC is a right triangle | 1.Given |
2.m∠A+m∠B=90° | 2.Sum of acute angles in right triangle is 90° |
3.m∠A=90°-m∠B | 3.Subtraction Property of Equality |
4.¯CD is an altitude of ΔABC | 4.Given |
5.∠ADC is a right angle | 5.Definition of an altitude |
6.ΔADC is a right triangle | 6. |
7.m∠A+m∠ACD=90° | 7. |
8.m∠A=90°-m∠ACD | 8.Subtraction Property of Equality |
9.90°-m∠B=90°-m∠ACD | 9. |
10.-m∠B=-m∠ACD | 10.Subtraction Property of Equality |
11.m∠B=m∠ACD | 11.Multiplication Property of Equality |
12.∠B≅∠ACD | 12.Definition of congruent angles |
13.∠A≅∠A | 13.Reflexive Property of Congruence |
14. | 14.AA Similarity Theorem |
15.¯CD is an altitude of ΔABC | 15.Earlier result |
16.∠BDC is a right angle | 16.Definition of an altitude |
17.ΔBDC is a right triangle | 17.Definition of a right triangle |
18.m∠B+m∠BCD=90° | 18. |
19.m∠B=90°-m∠BCD | 19.Subtraction Property of Equality |
20.m∠A+m∠B=90° | 20.Earlier result |
21.m∠B=90°-m∠A | 21.Subtraction Property of Equality |
22.90°-m∠BCD=90°-m∠A | 22.Transitive Property of Equality |
23.-m∠BCD=-m∠A | 23.Subtraction Property of Equality |
24.m∠BCD=m∠A | 24.Multiplication Property of Equality |
25.∠BCD≅∠A | 25.Definition of congruent angles |
26.∠B≅∠B | 26.Reflexive Property of Congruence |
27. | 27.AA Similarity Theorem |
28. | 28.Ratios of corr. sides of sim. triangles equal |
29.BC2=AB⋅BD | 29.Multiplication Property of Equality |
30. | 30.Ratios of corr. sides of sim. triangles equal |
31.AC2=AB⋅AD | 31.Multiplication Property of Equality |
32.AB=AD+BD | 32. |
33.AB-BD=AD | 33.Subtraction Property of Equality |
34.AC2+BC2=AB⋅AD+AB⋅BD | 34. |
35.AC2+BC2=AB⋅(AB-BD)+AB⋅BD | 35.Substitution Property of Equality |
36.AC2+BC2=AB2-AB⋅BD+AB⋅BD | 36.Distribution Property of Equality |
37.AC2+BC2=AB2 | 37.Algebra (subtraction) |
A.
What is the missing reason in step 6?
- Definition of a right triangle
- Pythagorean Identity
- Sum of angles in a triangle equals 180°
- Given
B.
What is the missing reason in step 7?
- Given
- Angle Addition Postulate
- Consecutive Interior Angles Theorem
- Sum of the acute angles in a right triangle is 90°
C.
What is the missing reason in step 9?
- Addition Property of Equality
- Transitive Property of Equality
- Subtraction Property of Equality
- Corresponding angles of congruent triangles are congruent
D.
What is the missing statement in step 14?
- ΔACD ~ ΔCAB
- ΔACD ~ ΔBCA
- ΔACD ~ ΔABC
- ΔACD ~ ΔACB
E.
What is the missing reason in step 18?
- Given
- Angle Addition Postulate
- Consecutive Interior Angles Postulate
- Sum of the acute angles in a right triangle is 90°
F.
What is the missing statement in step 27?
- ΔABC ~ ΔCBD
- ΔABC ~ ΔCDB
- ΔABC ~ ΔDBC
- ΔABC ~ ΔDCB
G.
What is the missing statement in step 28?
- BCBD=BCAB
- BCBD=ABBC
- CDAC=ABBC
- ABCD=ABBC
H.
What is the missing statement in step 30?
- CDAB=ABAC
- BCAD=ABAC
- ACAD=ACAB
- ACAD=ABAC
I.
What is the missing reason in step 32?
- Segment Addition Postulate
- Given
- Midpoint of a line segment
- Perpendicular Bisector Theorem
J.
What is the missing reason in step 34?
- Binomial Expansion Theorem
- Addition Property of Equality
- Pythagorean Theorem
- Perimeter of a triangle