The following system of equations has only one solution, which is (2,0), because you can use the method of substitution to find the value of x and if it has multiple solutions.
y = x - 2
y = - x + 2
x - 2 = - x + 2
2x = 4
x = 2 (substituting this back into the equation)
y = 2 - 2
y = 0