Chapter 4: Pair of Linear Equations in Two Variables

Pair of Linear Equations in Two Variables solves two equations together to find their one shared solution — graphically, and algebraically by elimination and substitution — while also recognising, from the equations alone, whether a pair has one solution, none, or infinitely many.

A sign error while adding or subtracting the two equations is the most common slip in elimination; in substitution, it's forgetting to plug the found value back into the original equation rather than an intermediate one. This chapter is the direct payoff of Class 9's single-equation work — one equation's infinite solutions, narrowed to exactly one by combining it with a second, the way two crossing lines on a graph meet at exactly one point.