Rule 1:

If the solution of two equations is like 2=7, then the equations are not equilateral with no common solution.

Rule 2:

If the solution of two equations is like 0=0, then the equations are equilateral with infinite common solution.

Rule 3:

If the solution of two equations is like 2=2 or 7=7 or 9=9, then the equations have only one solution.

CB