Hi OldTimer :)
An aeroplane is observed at the same instant from three stations A,B, C in a horizontal straight line but not in a vertical plane through the aeroplane.
If AB=BC =c and the angles of elevation from A,B C are respectively alpha, beta and gamma prove that the height of the plane is
\(\frac{c\sqrt2 }{\sqrt{(cot^2\alpha +cot^2\gamma -2cot^2\beta )} }\)
I have not got my head around what this question is asking. Can you (or someone else) help with a pic?
this is the bit I am not understanding
"a horizontal straight line but not in a vertical plane"