Can systems of equations with the same slopes have infinitely many solutions?

Answer 1

Absolutely, but only if they're concurrent. This means that they not only share the same slope, but also share the same y-intercept, which results in the lines sharing every x-y coordinate. Concurrent is another way of saying the lines are actually just the same line. If they're not concurrent, then they're only parallel, so will have no solutions. For example:

Our system:

2x + 3y = 6

4x + 6y = 12

These two equations, when you put them in slope-intercept form, will have the same slope and the same y-intercept. This means they are concurrent, and their system will have infinitely many solutions. Notice that if you multiply the entire first equation by 2, you get the second equation. Concurrent lines always share this kind of relationship, where you can multiply one by some number to get the other.

Another system:

2x + 3y = 6

4x + 6y = 10

These two equations, when you put them in slope-intercept form, will have the same slope but will not have the same y-intercept. This means they are parallel, so their system will have no solutions. Notice that if you multiply the entire first equation by 2, the coefficients on x and y will be the same in both equations, but the constants on the right side will not. This relationship is shared by all parallel lines.