How do you know if a coordinate on a graph is positive or negative?

The positive is on the top right hand corner and the negative is the left lower corner.

Negative Slope. If a line has a positive slope (i. e. m > 0), then y always increases when x increases and y always decreases when x decreases. Thus, the graph of the line starts at the bottom left and goes towards the top right. Thus, as x increases by 3, y decreases by 4, and as x decreases by 3, y increases by 4.