State and prove Converse of Thales theorem
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Answer:
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Converse of Thales theorem
It states that if a line divides any two sides of the triangle in the same ratio, then the line is parallel to the third side
which means,
If AD/DB = AE/EC (Given)
=> DE is parallel to BC
Proof
Let us draw a triangle ABC and DE || BC
So, AD/DB = AE/EC {by thales theorem} ---> (1)
For some instance, let us assume that DE is not parallel to BC
Draw another point F on AC such that DF parallel to BC
By thales theorem,
AD/DB = AF/FC ----> (2)
From (1) and (2) :
AE/EC = AF/FC
Now adding 1 to both sides, we get
AE/EC + 1 = AF/FC + 1
=> (AE + EC) /EC = (AF + FC) /FC
=> AC/EC = AC/FC
* Cancelling AC from both side
=> EC = FC
This means that the length of EC is equal to FC
but we have drawn F not on E. Since the points doesn't coincide
∴ DE || BC
