How I can determine the intersection point of two projectile

Answer 1

[Torsten]

Set x1 = x2 and y1 = y2 for an intersection point of the two curves.

You'll get

xinter= (tan(theta2)-tan(theta1))/(g/(2*(v2*cos(theta2))^2)-g/(2*(v1*cos(theta1))^2))
yinter= tan(theta1)*xinter- g*xinter^2/(2*(v1*cos(theta1))^2) - y0

as intersection point.

Of course, you will have to check whether xinter > 0, yinter > 0.