River

From the observatory 11 m high and 24 m from the riverbank, river width appears in the visual angle φ = 13°. Calculate the width of the river.

Correct result:

y =  29.5 m

Solution:

h=11 m x=24 m A=13 rad=13 π180 =13 3.1415926180 =0.22689 rad B=arctan(x/h)=arctan(24/11)1.141 C=A+B=0.2269+1.1411.3679 rad c=180/π C=180/3.1416 1.367978.3764 tanC=(x+y)/h y=h tan(C)x=11 tan(1.3679)24=29.5 m



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