A single equation in two unknowns has infinitely many solutions; to find just one we need two equations that must hold at the same time.
Definition — System of equations
A system of equations is a set of two or more equations that must be satisfied simultaneously.
Solving the system means finding the values of the unknowns that satisfy all the equations at the same time.
Connections
Topics: Linear systems
Concepts: System of equations
Skills: Solving systems