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Answer» Given :- In triangle ABC, DE || BC
To Prove :- AD / BD = AE / CE
Construction :- Join DC, BE, draw DG Perpendicular to AC and EF Perpendicular to AB
Proof :-
ar (ADE) = AD × EF / 2 -----(1)
ar (BDE) = BD × EF / 2 ------(2)
On dividing equation 1 by 2, we get
ar ( ADE) / ar ( BDE) = AD / BD -------(3)
Similarly,
ar (ADE) / ar (DEC) = AE / EC ------(4)
But,
ar ( DEC) = ar ( BDE) ( They are on same base and between same PARALLEL lines)
On putting this value in equation (4), we get
ar (ADE) / ar (BDE) = AE / EC -------(5)
On comparing equation (3) and (5), we get
AD/BD = AE / EC
Hence Proved...
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