## 1. Locus of Circle x^{2} + y^{2} = a^{2}

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

4. Slope of the line m = tanθ

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 (x_{1} , y_{1} _{)} and (x_{2} , y_{2} ) is

6. If m_{1} and m_{2} are slope of any two lines L_{1} and L_{2} then

(a). If lines L_{1} and L_{2} are parallel to each other then m_{1} = m_{2}

(b). If lines L_{1} and L_{2} are perpendicular to each other then m_{1} . m_{2 = -1}

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

Slope (m) = Tan0^{0}

m = 0 ( Not Defined )

Slope of line PQ = 0

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

Slope (m) = Tan90^{0}

m = ∞ ( Not Defined )

Slope of line PQ = ∞

9. If a line is equally inclined to the axis , then it will make an angle of 45^{0} or 135^{0} with the positive direction of x – axis.

Slope = Tan45^{0 }

^{ or }

Slope = Tan135^{0}

Slope = ± 1

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