Mathematics for IGCSE & O level - Equations (Section 7 - No. 40)
If you want to solve a system of equations using substitution, what do you need initially?
Two equations with no variables.
Two equations with the same variables.
One equation already solved for a variable.
Both equations solved for the same variable.
הֶסבֵּר
Substitution starts best when one equation explicitly expresses a variable.