Summary

• Slope of a line joining by .
• If a line makes an angle with the positive direction of ,
• Slope of is zero, slope of is not defined.
• Parallel lines have same slope.
• If two lines are perpendicular, the product of their slopes = (âˆ’ 1).
• The acute angle between lines with slopes is given by .
• Three points A, B, C are collinear if slope of AB = slope of BC.
• The equation of is and that of is
• Any line parallel to at a distance units from it is given by any line parallel to at a distance of units from it has equation
• The general equation of a line is of the form where are not zero simultaneously. Slope of this line is .
• If is the slope and is the -intercept of a line, then its equation is
• The equation of a line having slope and passing through is given by: .
• The equation of a line joining the points
• A line with -intercept units and -intercept units has equation:
• The equation of a line having normal distance from the origin and the angle between the normal and the positive is .
• The perpendicular distance of a line from a point is given by
The perpendicular distance of (0, 0) from
• The distance between the parallel lines and is given by
• If two straight lines are parallel, then the coefficients of are proportional in their equations. In particular, the equations of two parallel lines differ only by a constant.
• The equation of straight line perpendicular to the line is of the form where is a constant.
• The equation of a straight line passing through the intersection of and is where is a constant.