You use substitution to solve a system of equations and, after simplifying the equations, end with an expression that says 0 = 4. What does that say about the lines and about the number of solutions to the system?
if you have 2 equations in two unknowns and the process of attempting to solve the system produces a contradiction such as 0 = 4, then there is no intersection of the lines. the result is a contradiction (zero never equals four). "no solution"
