Prove that the area of the parallelogram formed by the lines 3x – 4y + a = 0, 3x – 4y + 3a = 0, 4x – 3y – a = 0 and 4x – 3y – 2a = 0 is 
sq. units.
Given:
The given lines are
3x − 4y + a = 0 … (1)
3x − 4y + 3a = 0 … (2)
4x − 3y − a = 0 … (3)
4x − 3y − 2a = 0 … (4)
To prove:
The area of the parallelogram formed by the lines 3x – 4y + a = 0, 3x – 4y + 3a = 0, 4x – 3y – a = 0 and 4x – 3y – 2a = 0 is 
sq. units.
Explanation:
From Above solution, We know that
Area of the parallelogram
⇒ Area of the parallelogram
square units
Hence proved.
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