How do i give a "parametrization for the curve": the ray with initial point (2,5) that passes through (-1,0)?

To parametrize a curve, you are looking for some functions that relate to y and x.
y = f(t)
 x = g(t)

if you bind on t
The easiest way to do this is to write your original function y = f(x),
 then let
x = t
So you have x = t, and
y = f(t) as your parametrization.