# Formulas and Results of Straight Lines

Consider two points and then

**01.** The distance formula

**02.** Midpoint formula

**03.** The point dividing in the ratio is

**04.** Slope of is

**05.** Slope of x-axis = zero

**06.** Slope of line parallel to x-axis = zero

**07.** Slope of y-axis is not defined i.e.

**08.** Slope of line parallel to y-axis is not defined i.e.

**09.** Equation of x-axis is

**10.** Equation of x-axis is

**11.** Equation of the line parallel to x-axis and at a distance is.

**12.** Equation of the line parallel to y-axis and at a distance is.

**13.** Equation of the line with slope and y-intercept is , which is called slope – intercept form.

**14.** Equation of the line passing through and having the slope is , which is called slope – point form.

**15.** Equation of the line passing through two points and is

.

**16.** Equation of the line having and as x – intercept and y – intercept is and is called the equation of the line in intercept form.

**17.** Normal form of the straight line is , where is the length of the perpendicular from to the line, and is the inclination of the perpendicular.

**18.** General form of the equation of a straight line is Consider two lines and having the slopes and respectively.

**19.** If two lines and are parallel, then .

**20.** If two lines and are parallel, then .

**21.** Angle from to is

**22.** Distance of point from the line is

.

**23.** If with , is the equation of the line , the lies:

**(1)** above the line if

**(2)** below the line if

**(3)** on the line if

**24.** Three lines , , are concurrent if