Hello friends, is it possible to find initial velocity purely from launch angle and final horizontal displacement?
Yes it is possible.
Start d^2x/dt^2 = 0 and d^2y =dt^2 = 0.
After integration you will end up with
x = V*cos(theta)*t # eq 1
y = (-gt^2)/2 + Vsin(theta)t # eq 2
Substitute x* i.e. final displacement. This will mean y=0 assuming we are dealing with flat plain.
Now you have two equations with two unknowns. Solving these two equations you can find the final time and the speed V which you could then use find the initial velocity.