30 points and brainliest which counterexample disproves the following statement? if a line has a y-intercept of 0, then it has a negative slope. 1) y=2x+1 2) y=2x-1 3) y=2x 4) y=-2x

A counter-example is an concrete example (or case) which disagrees with a given statement.  It takes a single counter-example to disprove any given statement.

There are only two lines that have a y-intercept of zero (the condition of the statement), namely
y=2x and
y=-2x.

Out of these, one has a positive slope (2) and the other has a negative slope (-2).

Therefore the only line that is a counter example is the one with a positive slope, or
y=2x