Focus and Slope Formula

1. Locus of Circle x2 + y2 = a2Locus of Circle

Centre =  (0 ,0)

Radius of Circle = a

2. Slope of line ax + by + c = 0 is m = – a/b

3. If three points A , B and C are collinear then 

If three points A , B and C are collinear

4. Slope of the line m = tanθ 

Slope of the line

where θ is angle which makes with the positive direction of the x – axis in anticlockwise direction.

5. Slope of the line which passing through points (x1 , y1 ) and (x2 , y2 ) is 

Slope of the line which passing through points

6. If m1 and m2 are slope of any two lines L1 and  L2 then 

(a). If lines L1 and  L2 are parallel to each other then m1 = m2

If lines L1 and  L2 are parallel to each other then m1 = m2

(b). If lines L1 and  L2 are perpendicular to each other then m1 . m2 = -1

If lines L1 and  L2 are perpendicular to each other then m1 . m2 = -1

7. If a line parallel to x – axis or perpendicular to y – axis then 

If a line parallel to x - axis or perpendicular to x - axis then 

Slope (m) = Tan00

m = 0  ( Not Defined )

Slope of line PQ = 0

8. If a line parallel to y – axis or perpendicular to x – axis then 

If a line parallel to x - axis or perpendicular to x - axis then 

Slope (m) = Tan900

m = ∞  ( Not Defined )

Slope of line PQ = ∞

9. If a line is equally inclined to the axis , then it will make an angle of 450 or 1350 with the positive direction of x – axis.

Slope = Tan450         

     or        

Slope = Tan1350

Slope = ± 1

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