mathmatic
marks -10
Diagonal Ac and BD of quadrilateral is
Intreset at o such that og op
i) AH.DOC = Ar AOB
in Ar.DOC AM.AOB
Answers
Answer:
iska answer hai 10 make ac and ab are ah.doc.aer
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Answer:
i)Let us draw DPperpendicular to AC and BQ perpendicular AC
In △DOP and △BOQ
∠DPO=∠BQO=90
∘
∠DOP=∠BOQ (vertically opposite angles)
OD=OB(given)
△DOP≅△BOQ(AAS congruence rule)
∴DP=BQ by CPCT .....(1)
and area(DOP)=area(BOQ) ......(2) since area of congruent triangles are equal.
In △CDP and △ABQ,
∠CPD=∠AQB=90
∘
CD=AB(given)
DP=BQ from (1)
∴△CDP≅△ABQ by RHS congruence rule.
⇒ area△CPD=area△AQB ........(3)since area of congruent triangles is equal.
Adding (2) and (3)
Area△(DOP)+Area△(CDP)=area△(BOQ)+area△(ABQ)
⇒ Area△(DOC)=Area△(AOB)
Hence proved.
In part (i) we proved that
Area△(DOC)=Area△(AOB)
Adding Area△(OCB) both sides,
Area△(DOC)+Area△(OCB)=Area△(AOB)+Area△(OCB)
⇒ Area△(DCB)=area△(ACB)
In part (ii) we proved
Area△(DCB)=area△(ACB)
We know that two triangles having same base and equal areas, lie between same parallels.
Here △DBC and △ABC are on the same base BC and are equal in area,
So, these triangles lie between the same parallels DA and CB
∴DA∥CB
Now, in △DOA and △BOC
∠DOA=∠BOC(vertically opposite angles)
∠DAO=∠BOC since DA∥CB,AC transversal, alternate angles are equal.
OD=OB(given)
∴△DOA≅△BOC (AAS congruency)
DA=BC by CPCT.
So, in ABCD, since DA∥CB and DA=CB
One pair of opposite sides of quadrilateral ABCD is equal and parallel.
∴ABCD is a parallelogram.
Explanation:
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