Find the value of x for which the expression 2

Home » Aptitude » Algebra » Question

Find the value of x for which the expression 2 – 3x – 4x² has the greatest value.

Expression = 2 – 3x – 4x²
= – (4x² + 3x – 2)

= −		(2x)² + 2 × x ×	3	+		3		²	−		3		²	− 2
			4			4					4

= −			2x +	3		²		+		3		²	+ 2
				4						4

The value of expression will be maximum if,

2x +	3	= 0
	4

⇒ 2x = −	3
	4

⇒ x = −	3
	8