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Mathematics
Mathematics
Problem
Prove that
3
O
D
+
D
A
+
D
B
+
D
C
3\mathbf{OD} + \mathbf{DA} + \mathbf{DB} + \mathbf{DC}
3
OD
+
DA
+
DB
+
DC
is equal to
O
A
+
O
B
−
O
C
\mathbf{OA} + \mathbf{OB} - \mathbf{OC}
OA
+
OB
−
OC
.
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