from the first:
t = x/(vcosØ)
from the 2nd:
y = vsinØ(x/(vcosØ) - (g/2)(x^2/(v^2 cos^2 Ø)
y = xtanØ - (gx^2)/(2v^2cos^2 Ø)
Eliminate t from the two equations
x = vtcos(theta)
and
y = vtsin(theta) - (gt^2/2)
and obtain a relationship between x and y (assume that v, g and theta are constants)
2 answers
You can also read the excellent article on "trajectory" in wikipedia, where these equations are derived.