If for non-zero x, x2 – 4x

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x² – 4x –1 = 0
⇒ x² – 1 = 4x

⇒	x² – 1	=	4x
	x		x

⇒ x –	1	= 4
	x

On squaring both sides,

	x −	1		²	= 16
		x

⇒ x² +	1	− 2 = 16
	x²

⇒ x² +	1	= 16 + 2 = 18
	x²

If for non-zero x, x² – 4x –1 = 0, the value of x² +	1	is :
	x²