a projecticle is launched, with angle of elevation @, from an origin O on level ground. At t seconds, its horizontal and vertical displacement, x and y metres respectively, are given by:
x = 20tcos@, y = -5t^2 + 20tsin@
a) show by eliminating @, that x^2 + (y +5t^2)^2 = 400t^2
b) hence or...