Mathematics for IGCSE & O level - Equations (Section 6 - No. 9)
When would you use substitution to solve a system of equations?
When one equation is already solved for a variable.
When both equations are linear.
When the coefficients of the variables are easy to manipulate.
When the coefficients of the variables are fractions.
Uitleg
Substitution is best when one equation is pre-solved for a variable.