Many locus problems involve a parameter t (like the parameter of a parabola or the slope of a variable line). Strategy:

1. Express the coordinates of the moving point in terms of t: x = f(t), y = g(t).
2. Eliminate t between these two equations.
3. The resulting equation in x,y is the locus.

Example: A variable chord of $y^2$=4ax is such that the tangents at its endpoints meet at a right angle. Find the locus of the midpoint. Use parametric points ($at^2$, 2at), express midpoint in terms of t1, t2, apply the perpendicular tangent condition t1*t2=-1, and eliminate.