If x = 5 − √21, then the value of √x

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√x = √5 − √21

⇒ √x =	√10 − 2√21
	√2

=	√7 + 3 − 2 × √7× √3
	√2

=	√7 − √3
	√2

√32 − 2x = √32 − 2 ( 5 − √21)
= √32 − 10 + 2√21)
= √22 + 2√21)
= √21 + 1 + 2 × √21 × 1
= √21 + 1

=	√7 − √3
	√2(√21 + 1 − √21)

=	1	= √7 − √3
	√2

If x = 5 − √21, then the value of	√x	is
	√32 − x − √21

1	(√3 − √7)
√2

1	(√7 − √3)
√2

1	(√7 + √3)
√2