I would have assumed that you've run into these cases by now.
There are three possible outcomes.Describe all possible outcomes of solving a system of two equations.
 The system has a unique solution.
The solution is: .
The problem asks for two numbers whose sum is 8 and whose difference is 2.
. . The numbers are 5 and 3.
If we graph the two lines, they intersect at (5,3).
 The system has no solutions.
If we try to solve the system, we get a false statement, like: .
. . This indicates that the system has no solution.
The problem asks for two numbers whose sum is 4 and whose sum is 3.
. . Of course, there are no such numbers.
If we graph the two line, we find that they are parallel.
. . They do not intersect.
 The system has infinite soluions.
If we try to solve the system, we get a true statement, like: .
. . This indicates that the system has infinitely many solutions.
The problem says: find two numbers whose sum is 4
. . and if we double the numbers and add them, we get 8.
We see that is a solution . . . but so is
If we graph the lines, we get the same line twice.
. . So, of course, they "intersect" each other a zillion times.