Two column proof for this figure?? (question in the link)http://i47.tinypic.com/2a7c513.jpg

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embizze | High School Teacher | (Level 1) Educator Emeritus

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We are given isosceles `Delta ABC` with vertex A, altitudes `bar(CE),bar(BD)` . We are asked to prove that `Delta HBC` is isosceles, where H is the intersection of the altitudes.

** Depending on the text and/or instructor, you may have to include more/less detail. **

Statement:                                Reason:

(1) `bar(AB) cong bar(AC)`                           (1) Given

(2) `/_ABC cong /_ACB`              (2) Isosceles triangle theorem *

(3) `/_CEB,/_BDC` are rt angles (3) Definition of altitude

(4) `/<CEB cong /_BDC`               (4) Rt angles are congruent

(5) `bar(BC) cong bar(BC)`                           (5) Reflexive property of `cong`

(6) `Delta BEC cong Delta CDB`                (6) AAS

(7) `/_DBC cong /_ECB`               (7) CPCTC **

(8)`` `bar(HB) cong bar(HC)`                         (8) converse of isos. triangle thm*

(9) `Delta HBC` is isosceles             (9) Definition of isosceles

QED.

* Isosceles triangle theorem -- If two sides of a triangle are congruent then the angles opposite those sides are congruent.

** CPCTC -- corresponding parts of congruent triangles are congruent

* Converse of isosceles triangle theorem -- If two angles of a triangle are congruent, then the sides opposite those angles are congruent

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