Let, AB is the tree,

∠DEB =β

∠CEB=β-α where, ∠DEC=α

In triangle ECD,

exterior ∠ECB=interior (∠CED+∠EDC)=90°+α

In triangle ABC,

exterior ∠EAB=interior ∠ACB+∠ABC = 90°+α+Θ= 90°+(α+Θ)

Now in triangle, AEB,

AB/Sin ∠AEB=EB/Sin ∠EAB

AB= EB. Sin ∠AEB/Sin ∠EAB

AB= EB.Sin(β -α)/Sin 90°+(α+Θ)

AB= EB.Sin(β -α)/ Sin (α+Θ)