prove BPT theorem (Thales theorem )
Answers
Answer:
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Answer:
AD/DB = AE/EC
Explanation:
> If a line drawn parallel to one side of a triangle to intersect the other two sides in distinct points, the other two sides are divided in the same ratio.
GIVEN :
∆ABC Where DE || BC
TO PROVE:
AD/DB = AE/EC
CONSTRUCTION:
Join BE and CD
Draw DM perpendicular AC
EN Perpendicular AB
PROOF:
ar(ADE) = 1/2 × base × height
= 1/2 × AD × EN ......(1)
ar(BDE) = 1/2 × base × height
= 1/2 × DB × EN ......(2)
ar(ADE) = 1/2 × base × height
= 1/2 × AE × DM ....(3)
ar(DEC) = 1/2 × base × height
= 1/2 × EC × DM .....(4)
> DIVIDE (1) & (2)
ar(ADE) / ar(BDE)
= 1/2 × AD × EN / 1/2 × DB × EN
= AD/DB......(A)
>DIVIDE (3) & (4)
ar(ADE) / ar(DEC)
= 1/2 × AE × DM / 1/2 × EC × DM
= AE / EC......(B)
NOW,
∆BDE and ∆DEC are on the same base DE and between the same parallel lines BC and DE
= ar(BDE) = ar(DEC)
Hence,
ar(ADE) / (BDE) = ar(ADE) / ar( DEC)
= AD/DB = AE/EC
( from A & B )
HENCE PROVED...