Straight lines are the most fundamental objects in coordinate geometry. In the Cartesian plane, every straight line is described by a linear equation in two variables x and y. The study of straight lines encompasses determining equations from given conditions, computing distances and angles, and analyzing special configurations like concurrent lines, angle bisectors, and pairs of lines. For JEE Main, straight lines contribute 1-2 questions per year, typically testing the distance formula, family of lines, and reflection/image problems. The topic serves as a prerequisite for circles, conics, and 3D geometry, making it essential to master early. Key skills include converting between different forms of line equations, applying the perpendicular distance formula efficiently, and using the family of lines approach to avoid tedious computations. The pair of straight lines represented by second-degree equations is a uniquely JEE-focused topic that combines algebraic manipulation with geometric insight.