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Mathematics
Mathematics
Problem
A
B
C
D
E
ABCDE
A
B
C
D
E
is a pentagon, prove that
A
B
+
B
C
+
C
D
+
D
E
+
E
A
=
0
\mathbf{AB} + \mathbf{BC} + \mathbf{CD} + \mathbf{DE} + \mathbf{EA} = 0
AB
+
BC
+
CD
+
DE
+
EA
=
0
.
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