Final Cover - For Printing

As the child is already familiar with the idea of perpendicularity, its nature relating to

slope of a line alone needs explanation.

5. Equation of a straight line
   The equation of any line passing through the origin is of the form y = mx. If a straight
   line intersects the axes then the line segments cut off on the axes by the line are
   called the intercepts.

There are several forms of equations of straight lines of which the following are few.

(i) Slope intercept form
The equation of a line with slope m and y – intercept c is given by
y = mx + c

(ii) Slope - one point form
The equation of a line passing through a point (x 1 ,y 1 ) and having slope ‘m’ is,
y – y 1 = m(x – x 1 )

(iii) Two points form
The equation of the line passing through the two points (x 1 ,y 1 ) and (x 2 ,y 2 ) is given by,

(^211) x 2 - x^11
x-x
y y
y y =
−

−

(iv) Intercepts form
The equation of the line having x-intercept ‘a’ and y- intercept ‘b’ is given by,

Note :

The four equations mentioned above are all first degree equations in x and y. Note that

the general first degree equation in x and y always represents a straight line. Hence the

general equation of a straight line is ax + by + c = 0, with atleast one of a or b is

different from c.