Give an example of an equation with an infinite number of solutions. Then make one change to the equation so that it has no solution

X^2 + y^2 = 1 is one equation with an infinite number of solutions.

x^2 + y^2 = - 1 has no real solutions. The only change was the sign of 1.

Two equations with infinite solutions would look the exact same. Example:

y=mx+b

y=mx+b

Example 2

y=2x+5

y=2x+5

For an equation with no solution they would have the same slope but different y intercepts. An equation with same slope and same y intercepts would have infinite solutions.