Q)  In the given figure, ∠ CEF = ∠ CFE. F is the midpoint of DC. Prove that \frac{AB}{BD} = \frac{AE}{ FD}.

In the given figure, ∠ CEF - ∠ CFE. F is the midpoint of DC. Prove that AB / BD = AE / FD. 10th CBSE

Ans:

Step 1: From given conditions:

  1.  ∵  ∠ CEF = ∠ CFE

∴ CE = CF (sides of opp. Angles)

2. ∵  F is midpoint of CD

∴ FD = CF

CE = CF = FD ……… (i)

Step 2: Construct to find relation:

Let’s draw DG ǁ BE

∴ by Basic Proportionality Theorem in Δ ABE:  \frac{AB}{BD} = \frac{AE}{GE}  ………… (ii)

Step 3: establish co-relation:

∴ by Mid Point Theorem in Δ GDC :  \frac{DF}{FC} = \frac{GE}{CE}

∵  DF = FC ……. from equation (i)

\frac{DF}{FC} =  1 =  \frac{GE}{CE}

∴ GE = CE

∵  CE = CF = FD ….. from equation (i)

CE = CF = FD = GE  ……. (iv)

Step 4: Proving the relation:

∵  \frac{AB}{BD} = \frac{AE}{GE}   ……. from equation (ii)

and GE = FD ………… from equation (iv)

∴  \frac{AB}{BD} = \frac{AE}{FD} 

Hence Proved!

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