When at least one of the equations is already solved for one of the variables.
When the coefficient of one of the variables is small in at least one of the equations.
In the case of large or fractional coefficients, it becomes difficult to use this method. Let's have a look at an example of a system of equations for each situation.
Situation
Example
Explanation
1. At least one of the equations is already solved for one of the variables.
y=2x-4 2y+3x=3
Here the first equation is already solved, so we substitute y=2x-4 into the second equation and then solve it.
2. The coefficient of one of the variables is small in at least one of the equations.
5y+3x=-16 3y+x=4
The coefficient of x is 1 in the second equation. We can isolate it and then substitute it into the first equation.
