Given: ABCD is a quadrilateral and BD is one of its diagonals.
To Prove: ABCD is a parallelogram and to determine its area.
Proof: ∠ABD = ∠BDC (= 90°) | Given But these angles form a pair of equal alternate
interior angles for lines AB, DC and a transversal BD AB || DC
Also, AD = DC (= 3 cm) | Given
Hence, quadrilateral ABCD is a parallelogram. A quadrilateral is a parallelogram if its one pair of opposite sides are parallel and equal Now,
ar(||gm ABCD) = Base x corresponding altitude
= 3x4 = 12 cm2
In the given figure, ABED is a parallelogram in which DE = EC. Show that area (ABF) = area (BEC)
In the following figure, ABCD is a parallelogram and EFCD is a rectangle. Also, AL ⊥ DC. Prove that
(i) ar(ABCD) = ar(EFCD)
(ii) ar(ABCD) = DC x AL.