A is given. If lines are drawn through parallel respectively to the sides and forming as shown in the adjoining figure, show that


Here given that BC || QA and CA || QB which means that BCQA is a parallelogram.


BC = QA (1)


Similarly, BC || AR and AB || CR, which means BCRA is a parallelogram.


BC = AR …(2)


But QR = QA + AR
From (1) and (2), we get,
QR = BC + BC


QR = 2BC


Hence, BC = QR


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