Determine slopes from points and graphs, recognizing positive, negative, zero, and undefined slopes, and write equations of lines in slope-intercept, point-slope, or standard form, including horizontal and vertical lines and parallel or perpendicular relationships. Use the distance and midpoint formulas for points in the two-dimensional Cartesian plane, and determine or interpret circle equations in standard form using their centres and positive radii. Solve coordinate geometry problems involving lines and circles by applying slope, distance, midpoint, substitution, and elimination to find unknown coordinates, intersections, parallel or perpendicular relationships, tangency, and zero, one, or two intersection points.