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9) Prove that a quadrilateral is a parallelogram if a pair of opposite sides is equal and parallel. |
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Answer» ong>Answer: GIVEN: ABCD is QUADRILATERAL and AB║CD, AB=CD. To prove: ABCD is a parallelogram Proof: AC is a transversal and ALSO AB║CD, therefore ∠BAC=∠DCA(ALTERNATE angles) In ΔADC and ΔCBA, we have AB=CD(Given) ∠BAC=∠DCA(Alternate angles) AC=CA(Common) ΔADC≅ΔCBA by the SAS rule. Hence, by CPCT, DA=BC Thus, Both the pair of opposite sides are equal in the quadrilateral ABCD, therefore ABCD is a parallelogram. Hence proved. |
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