In the system ax+2y=5 3x-6y=20 if there is one solution a cannot be:

In the system ax+2y=5 3x-6y=20 if there is one solution a cannot be:
Answer: "-1"

For the system ax+2y=5 and 3x-6y=20 to have one solution a=-1 causes linear dependence preventing a unique solution. This concept is critical in linear algebra for ensuring system solvability.