Height of hill when angle of elevation for each vertex is same 
The angle of elevation of the top of a hill from each of the vertices $A, B$ and $C$ of a horizontal triangle is ​​$\alpha$. Prove that the height of the hill is $\frac{a}{2} \tan\alpha \csc(A)$.

Could someone help me to approach this question. I am not getting how to start.

radius of circumcentre                                                                       R= a/2sinA =b/2sinB= c/2sinC IN WHICH AH = BH =CH= R
