Question

An aeroplane at an altitude of 300 m observes the angles of depression of opposite points on the two banks of a river to be 45degree and 60degree. Find the width of the river.

Answer 1

Hii frnd...

As we know tan= perpendicular/base
So,here
tan 45=300/base
1=300/base
base=300m.

tan 60=300/base
$\sqrt{3}$=300/base
base=300/$\sqrt{3}$
base=300$\sqrt{3}$/3
base=100$\sqrt{3}$m

Now add both the bases
300+100$\sqrt{3}$m (Either leave it here or...)
300+100(1.73)
300+173
473m

Here is your answer.

Hope it helped u!!!

Answer 2

height=300m
angle of depression=45,60

there will be two tringles ABD and ADC 
let the base be B
tan45=1
1=300/b
B=300
in TRINGLE ADC
let the base be b'
tan60=under root 3
under root 3=300/
B'=300/ under root 3
therefore width of the river =B+B'
=300+300/under root 3