Question

A bridge perpendicular along a river.Going some distance from the river along the one end of bridge,the other end of the bridge can be seen at 45 degrees. if we crosses 400 meters further,the end where we start can be seen at 30 degrees.Length of bridge??

There is a bridge perpendicular along a river.After going some distance from the river along the one end of bridge,the other end of the bridge can be seen at 45 degrees. if we crosses 400 meters further,the end where we start can be seen at 30 degrees. Let's determine the length of the bridge?
Please attach a pic

Answer 1

AB = L m is the length of the bridge.
After going at a distance from one end of the bridge (B ) along the river the other point of A of the bridge is seen at angle `45^@` from C.

Again crossing 400 m the point B is viewed at an angle `30^@` from D.

So `CD=400m and/_DBC=30^@`

Now `(AB)/(BC)=tan45^@=1`

So `BC=AB=L`

Again `(BC)/(CD)=cot30^@=sqrt3`

`=>L/400=sqrt3`

`=>L=400sqrt3=692.8m`