I have the following equation which describes a water jets trajectory. Vx=Cos(50) * 6.5m/s Vy=Sin(50) * 6.5m/s x=Vx*t y=Vy*t-0.5*g*t^2 where t=time Now, this plots a curve very well starting from zero. I want a line, starting from 0 also, that intersects the curve. Now, I have used the equation y=tan(35)*x where x is the distance across the bottom of the graph (x axis) on the adjacent part in the trig. So, to find the intersect, i need to get the curve equation in terms of x and y instead of y and t, so i have re-arranged; t=x/Vx and subbed in to give; y=Vy*(x/Vx)-0.5*9.81*(x/Vx)^2 If I equal them to one another; tan(50) *x = Vy*(x/Vx)-0.5*9.81*(x/Vx)^2 and re-arrange for x, i get; (tan(35)*Vx^2)/(-0.5*g)) - ((-Vx*Vy/(0.5*g)) = x = 0 Now, there is an intersect at 0, but not the one i want. Attached is a graph of both the line and curve, with 50 degrees angle on the jet, and 35 degrees on the line. Please help, ive been stuck on this alllll day, and alot of yesterday too!