A Venn diagram sorts equations of straight lines. One circle is 'parallel lines' and the other is 'lines with the same y-intercept'. Parallel lines only: y = 3x + 2 and y = 1 + 3x. In both circles: y = 3x - 5. Same y-intercept only: y = -5 + 2x and y = -5 - 3x. State where the equation y = 2x + 1 should be written: in the parallel lines circle only, in the same y-intercept circle only, in the overlap, or outside both circles.