Substitution
Make one variable the subject (e.g., ) and substitute into the other equation.
Linear & Quadratic
Always rearrange the linear equation first. Substituting quadratic into linear is harder.
Discriminant
determines intersections of and curve.
Tangents
If a line is tangent to a curve, their combined quadratic has .
Intersection Points
Solve for , then find corresponding . Coordinates are , .
Elimination
Useful for two linear equations. Add/Subtract equations to remove a variable.