What number must be added to the expression 16a2 –12a

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What number must be added to the expression 16a² –12a to make it a perfect square ?

1. 9
  4
2. 11
  2
3. 13
  2
4. 16

Correct Option: A

a² – 2ab + b² = (a – b)²
∴ 16a² – 12a

= (4a)² – 2 × 4a ×	3
	2

Hence, on adding		3		²	=	9	,
		2				4

expression will be a perfect square.