If there is only one solution for the two equations and , then cannot equal .
Find the value of
that implies the system has infinitely many solutions.
That is precisely the value that must not equal if the system has a unique solution.
The system , has infinitely many solutions.
That is, the ratio of the coefficients of and must be equal.
So, , has infinitely many solutions
Cross multiply to find .
Therefore, if the system has a unique solution, must not equal 10.