Q. 273.7( 10 Votes )

# From a point 100

Answer :

The figure for the question is Let A be the point 100 m above lake and C be the helicopter and C' be the reflection of helicopter in water.

Given,

Angle of elevation of helicopter from point A, ∠CAQ = 30° [Let θ1]

Angle of depression of reflection from point A, ∠QAC' = 60° [Let θ2]

Also,

AB = PQ = 100 m …

AQ = BP …

CP = CP' [image distance is equal to object distance]

And let CQ = 'x'

CP = CQ + PQ = 100 + x

⇒ CP' = 100 + x …

In ΔACQ  From ⇒ BP = x√3 m …

In ΔAQC'   [From ]

3x = x + 200

⇒ 2x = 200

⇒ x = 100 m

And

Height of helicopter above lake = CP = x + 100

= 100 + 100 = 200 m

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