posted by cyril .
. A surveyor wishes to measure the distance across Pasig River. She sets up her transit at a point C on the bank of the river, and sights on a point B on the other bank directly opposite her. Then she turns the transit through a right angle, and measures off a distance of 100 meters to a point A. She moves the transit to A, and measures the angle CAB, which is 50deg 11min 10 sec. How wide is the river?
draw the diagram, and it is clear that the distance x is
x/100 = tan 50°11'10"