Question

A man on the top of a rock on a seashore observes a boat coming towards it. If it takes 20 minutes for the angle of depression to change from 30 degree to 60 degree, how soon will the boat reach the shore?​

Answer 1

Step-by-step explanation:

AB is the rock C and D be the two possitions of the boat

∠ADB=60

0 ;∠A=30

0 ;CD=y;DB=y

tan30 0 =

x+yA = 31

⇒AB= 3x+y

Also tan60 0 =yAB

⇒AB= y∴ 3x+y

= 3 y or 2x =y

The boat takes 10 minutes to cover distance

x So it will take 5 minutes to cover

2x

∴ Time to reach B=(10+5) min = 15

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