Proofs Review

What’s in a Proof? Statement of the original problem     Diagram, marked with "Given" information       Re-statement of the "Given" information in the proof    Complete supporting reasons for each step in the proof       The "Prove" statement as the last statement  

Strategies For most proof problems, it is very helpful to examine the problem backwards -- from the "Prove" statement back to the "Given" information. 

Where does the conclusion come from?

Formal Proof Statements Reasons 1. Given 2.  Reflexive Property - a quantity is      congruent to itself. 3.  SAS:   If 2 sides and the include angle      one triangle are congruent respectively      to 2 sides and the included angles of a      second triangle, then the 2 triangles are      congruent. 4.  CPCTC: Corresponding parts of      congruent triangles are congruent.                                                           QED

Let’s Practice! Look at the following examples of given information and try to come up with some ideas about what conclusions can be drawn from that information. http://www.regentsprep.org/Regents/math/geometry/GP3/preproof.htm

Unscramble the Proof On the following slide is a proof from the problem below. Unscramble it with your partner. Given:         ABCD is a parallelogram              Prove:       DEFC is a rectangle

Statement Reason In a plane, two lines perpendicular to the same line are parallel. DEFC is a parallelogram If both pairs of opposite sides of a quadrilateral are parallel, the quadrilateral is a parallelogram. ABCD is a parallelogram Given Given DEFC is a rectangle If one angle of a parallelogram is a right angle, the parallelogram is a rectangle. <DEB is a right angle Perpendicular lines meet to form right angles. A parallelogram had 2 sets of opposite parallel sides.

Homework Continue working on your projects as outlined on ms-troast.wikispaces.com Create a proof with a solution and bring it to class next session. Complete 6 more sets of Khan Academy Reviews.