parallelograms on the same base and between the same parallels are equal in area
Answers
Step-by-step explanation:
Given two parallelogram ABCD and EFCD that have the same base CD and lie between same parallel AF and CD.
We have prove that ar(ABCD)=ar(EFCD)
Since opposite sides of ∥gm are parallel AB∥CD and ED∥FC with transversal AB
⇒∠DAB=∠CBF [ Corresponding angles ]
with transversal EF
⇒∠DEA=∠CFE [ Corresponding angles ]
⇒AD=BC [ Opposite sides of parallelogram are equal ]
In △AED ξ △BFC
⇒∠DEA=∠CFE
∠DAB=∠CBF
∴AD=BC
⇒△AED≅△BFC [ AAS congruency ]
Hence, ar(△AED)=ar(△BFC)
( Areas of congruent figures are equal )
⇒ar(ABCD)=ar(△ADE)+ar(EBCD)
=ar(△BFC)+ar(EBCD)
=ar(EBCD)
∴ar(ABCD)=ar(EBCD)
Hence, the answer is proved
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parallelograms on the same base and between the same parallels are equal in area
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Two ||gms ABCD and ABEF on the same base AB and between the same parallels AB and FC
ar(||gm ABCD)= ar(||gm ABEF).
In ∆ADF and ∆BCE, we have:
AD = BC (opp.sides of a ||gm)
∠ADF = ∠BCE (corresponding ∠s)
DF = CE ⠀⠀∴ DC = FE (each equal to AB)
⠀⠀⠀⠀⠀⠀⠀⠀⇒DC - FC = FE - FC ⇒ DF = CE
∴ ∆ADF ≅ ∆BCE (SAS-criterion).
And so, ar(∆ADF) = ar(∆BCE)
⠀⠀⠀⠀(congruent figures have equal areas).
Now, ar(||gm ABCD) = ar(∆ADF) + ar(quad.ABCF)
⠀⠀⠀⠀=ar(∆BCD) + ar(quad.ABCF)
⠀⠀⠀⠀⠀⠀⠀=ar(||gm ABEF).
Hence, ar(||gm ABCD) = ar( ||gm ABEF).
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