EQUATION OF THE LINE
– Mostly depends on different format those under one of the following
1. EQUATION OF A POINT AND SLOPE.
Let point be 
and slope be M.
-Let the two points being denoted as A
and B 
-Consider the figure below
For the line only if
= 
Multiply by 
both side
= 
3. EQUATION OF A SLOPE AND Y – INTERCEPT FORM
– -Consider the slope 
and 
– intercept, 
4. EQUATION OF 2 INTERCEPTS FORM
-Let consider X – intercept C, and Y intercept B
5. FAMILY EQUATION
– Is the equation formed from intersection of two lines passing through a certain points.
E.g. equation for intersection of L1 and L2 passing through points (a,b) can be obtained by using the formula.
Where K is constant
*
Important steps of determining family equation.
1. Solve for K by regarding equations of two lines and the point passing through.
2. Form family equation by using the value of K without regarding the point passing through.
Example.
1. Find the equation passing through the point (2,3) from the intersection to provided
Solution.
Point 
But,
(
From
The equation is 
ANGLE BETWEEN TWO LINES
-Let consider 
and 
where Q is angle made between 
and 
and 
is the angle of 
and 
is the angle of 
.
-Consider the figure below
Our intentions to find the value of 
which always should be acute angle.
where
