To Prove: ar(ΔAOD) = ar(ΔBOC).
Proof: ∵ ΔABD and ΔABC are on the same base AB and between the same parallels AB and DC.
∴ ar(ΔABD) = ar(ΔABC)
Two triangles on the same base (or equal bases) and between the same parallels are equal in area ⇒ ar(ΔABD) – ar(ΔAOB)
= ar(ΔABC) – ar(ΔAOB)
| Subtracting the same areas from both sides ⇒ ar(ΔAOD) = ar(ΔBOC).
In figure, ABCDE is a pentagon. A line through B parallel to AC meets DC produced at F. Show that
(i) ar(ΔACB) = ar(ΔACF)
(ii) ar(□AEDF) = ar(ABCDE).
Show that the area of a rhombus is half the product of the lengths of its diagonals.
Or
Prove that the area of a rhombus is equal to half the rectangle contained by its diagonals.