Hello, sakibniaz!
Did you make a sketch?
The angle of depression of a boat 50m from the base of a cliff is 30°.
How high is the cliff? . Give your answer correct to 3 decimal places. Code:
A * - - - - - - - - - - D
| * 30°
| *
| *
h | *
| *
| *
| 30° *
C *-----------------------* B
: - - - - 50 - - - - - :
The cliff is: $\displaystyle h = AC$
The boat is at $\displaystyle B\!:\;\;\angle DAB = 30^o$
.Hence: .$\displaystyle \angle ABC = 30^o$
In right triangle $\displaystyle ACB\!:\;\;\tan 30^o \:=\:\frac{h}{50}$
Now solve for $\displaystyle h.$