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AMSCO'S Geometry. New York - Rye High School

AMSCO'S Geometry. New York - Rye High School

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An Inequality Involving an Exterior Angle of a Triangle 279Solutiona. CDBb. DCA and Ac. The measure of an exterior angle of a triangle is greater than the measureof either nonadjacent interior angle.d. The whole is greater than any of its parts.EXAMPLE 2Given: Right triangle ABC, mC 90,BAD is an exterior angle at A.CProve: BAD is obtuse.ABDProof Statements Reasons1. BAD is an exterior angle. 1. Given.2. mBAD mC 2. Exterior angle inequalitytheorem.3. mC 90 3. Given.4. mBAD 90 4. Substitution postulate forinequalities.5. mBAD mBAC 180 5. If two angles form a linear pair,then they are supplementary.6. 180 mBAD 6. The whole is greater than any of itsparts.7. 180 mBAD 90 7. Steps 4 and 6.8. BAD is obtuse. 8. An obtuse angle is an angle whosedegree measure is greater than 90and less than 180.

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