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AMSCO'S Geometry. New York - Rye High School

AMSCO'S Geometry. New York - Rye High School

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The Rectangle 391EXAMPLE 1Given: ABCD is a parallelogram with mA mD.Prove: ABCD is a rectangle.DCProofWe will prove that ABCD has a right angle.Statements1. ABCD is a parallelogram. 1. Given.Reasons2. AB CD2. A parallelogram is a quadrilateralin which two pairs of oppositesides are parallel.3. A and D are supplementary. 3. Two consecutive angles of aparallelogram are supplementary.4. mA mD 180 4. Supplementary angles are twoangles the sum of whose measuresis 180.5. mA mD 5. Given.6. mA mA 180 or 6. A quantity may be substituted for2mA 180its equal.7. mA 90 7. Division postulate.8. ABCD is a rectangle. 8. A rectangle is a parallelogramwith a right angle.ABEXAMPLE 2The lengths of diagonals of a rectangle are represented by 7x centimeters and5x 12 centimeters. Find the length of each diagonal.SolutionAnswerThe diagonals of a rectangle are congruent and therefore equal in length.7x 5x 122x 12x 67x 5 7(6) 5x 1 12 5 5(6) 1 125 425 30 1 125 42The length of each diagonal is 42 centimeters.

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