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Consider a triangular plot ABC with sides AB = 7 m, BC = 5m and CA = 6m. A vertical lamp-post at the mid point D of AC subtends an angle 30° at B. The height (in m) of the lamp-post is:

A

`(2)/(3)sqrt(21)`

B

`2sqrt(21)`

C

`7sqrt(3)`

D

`(3)/(2)sqrt(21)`

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A
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