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Mathematics
Mathematics
Problem
D
D
D
and
E
E
E
are the mid-points of the sides
A
B
AB
A
B
and
A
C
AC
A
C
, respectively of
△
A
B
C
\triangle ABC
△
A
B
C
.
D
E
DE
D
E
is produced to
F
F
F
. To prove that
C
F
CF
C
F
is equal and parallel to
D
A
DA
D
A
, we need an additional information which is (A)
∠
D
A
E
=
∠
E
F
C
\angle DAE = \angle EFC
∠
D
A
E
=
∠
E
F
C
(B)
A
E
=
E
F
AE = EF
A
E
=
E
F
(C)
D
E
=
E
F
DE = EF
D
E
=
E
F
(D)
∠
A
D
E
=
∠
E
C
F
\angle ADE = \angle ECF
∠
A
D
E
=
∠
E
C
F
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