An equation written in slope-intercept form is y=mx+b, where m is a constant equal to the slope. Parallel lines have the same slope. So a line parallel to y=-2x+3 is y=-2x+5. Perpendicular lines have slopes which are negative reciprocals of each other. So a line perpendicular to y=-2x+3 is y=1/2x+7. y=2x-1 is neither parallel of perpendicular to y=-2x+3.
