parabolic equation

i want to calculate a parabola.i know the first speed vector v (vx,vy), first position (0,0),just considering gravity (g=-9.8).

y=a*x^x+b*x+c

could someone help me to calculate a,b,c expressions with (vx,vy,g).

my result is:

a=g/(2*vx*vx);
b=vy/vx;
c=0

i don't know it's right or not.it seems to be right in topright quadrant(x开发者_Python百科>0,y>0), seems to be wrong in other three quadrant.

could someone help me.

So: x = vx*t + .5*0*t**2 and y = vy*t - .5*9.8*t**2

You can plug those into the graphinator and you'll end up with a line for x and a nice parabola for y.