Posted by **garry** on Thursday, January 15, 2009 at 9:55pm.

The high level bridge, a railway bridge that crosses the Oldman River is over 1km long. From one point on the river, the angle of elevation of the top of the bridge is 62.6 degrees. From a point 20m closer to the bridge, the angle of elevation of the top of the bridge is 72.8 degrees. How high is the brige above the river, to the nearest meter? i don't understand how to do this question.. please help!!:(

- trig -
**bobpursley**, Thursday, January 15, 2009 at 10:17pm
let h be height. Let d be the distance from the first observation to the bridge.

h/d=tan62.6

and

h/(d-20)=tan72.8

in the first equation

d=h ctn62.6

second equation

d=h ctn72.8 +20tan72.8

set these two equations equal, and solve for h.

- trig -
**Reiny**, Thursday, January 15, 2009 at 10:38pm
or....

Consider the triangle formed with 20 m as the base and the two lines forming the angles of elevation to the top of the bridge.

62.6 will be the interior angle and 72.8 would be an exterior angle at the 20 m base.

That would make the interior angle at the base 107.2 and the small angle at the top where the lines meet at the bridge equal to 10.2 degrees.

by the Sine Law we can find the length of the line formed by the 72.8 degree line of observation.

this then becomes the hypotenuse of a right angled triangle where h is the height of the bridge, the side found above is the hypotenuse and the base angle is 72.8.

A simple sine ratio will find the height.

## Answer this Question

## Related Questions

- Math, Trig - The high level bridge, a railway bridge that crosses the Oldman ...
- Math - trigonometry - A bridge is 70m long. From the ends of the bridge the ...
- algebra - You live near a bridge that goes over a river. The underside of the ...
- algebra - You live near a bridge that goes over a river. The underside of the ...
- algebra - You live under a bridge that goes over a river. the underneath side of...
- algebra - You live under a bridge that goes over a river. the underneath side of...
- math - The angle of elevation from a buoy to the top of a bridge is 19 degrees. ...
- physics - Shyanne (60 kg) has to walk across a single rope bridge to cross a ...
- math (trig) - from the top of a bridge over the burlington canal, maria looks ...
- Writing - How can I end this? ____ The bridge I made a model of is the Sydney ...

More Related Questions