In the king-post bridge here shown the span is feet, and feet.

What angle does make with ?

   To find , we need to write down the details as shown here:

   Law of Cosines is used to find

Law of Cosines formulas:

Since we want to find , we will use the #1 Law of Cosines formula.

Plug in the known values:

Simplify:

Subtract from both sides:

Divide both sides by :

Simplify:

Change to acos, which is the same as to find angle:

(Answer)