Unit-I: Sets and Functions
Unit-II: Algebra
Unit-III: Coordinate Geometry
Unit-IV: Calculus
Unit-V: Mathematical Reasoning
Unit-VI: Statistics and Probability

Parallel Lines and Perpendicular Lines

 L_1  and L_2 be two lines inclined in a same plane, where the angle between these two lines is zero, then  L_1  and L_2 is said to be parallel lines.

 L_1 \parallel L_2

Perpendicular Lines:

 L_1  and L_2 be two lines inclined in a same plane, where the angle between these two lines is  \dfrac{\pi}{2} ,  then  L_1  and L_2   is said to be perpendicular lines.

 L_1 \perp L_2

Theorem:

If a pair of lines  L_1  and L_2 have slopes  m_1  and m_2 respectively, then 

(i)  m_1=m_2\Leftrightarrow L_1 \parallel L_2   or  L_1 = L_2

(i.e., Either  L_1  and L_2 are parallel or  L_1  and L_2   are coincident lines )

(ii)  m_1m_2 =-1 \Leftrightarrow L_1 \perp L_2

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