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Question
In parallelogram ABCD, its diagonals intersect at point O. If OA = 6 cm and OB = 7.5 cm, find the length of AC and BD.

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Solution
∵ When diagonals AC and BD intersect each other at point O,
then OA = OC = `1/2` AC
and OB = OD = `1/2` BD
∴ OA = `1/2 xx` AC ⇒ AC = 2 × OA
⇒ AC = 2 × 6 cm = 12 cm,
and OB = `1/2 xx "BD"` ⇒ BD = 2 × OB
⇒ BD = 2 × 7.5 cm ⇒ BD = 15 cm
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