A tower subtends an angle alpha at a ...

A tower subtends an angle `alpha` at a point `A` in the plane of its base and the angle of depression of the foot of the tower at a point `b` metres just above `A` is `beta` . Prove that the height of the tower is `btanalphacotbeta` .

`b tan alpha cot beta`

`b cot alpha tan beta`

`b tan alpha tan beta`

`b cot alpha cot beta`

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