Question

if x=5-√21 find the value of x²+1/x²

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Answer 1

Step-by-step explanation:

x²+1/x²

1+2/x²

1+1/(5-√21)²

1+1/25+21-2√21

(47-2√21)/46-2√21

Answer 2

Step-by-step explanation:

x=5-√21

x²+1/x²=(5-√21)²+1/(5-√21)²

25+21-10√21+1/(25+21-10√21)

46-10√21+1(46+10√21)/(46-10√21)(46+10√21)

46-10√21+(46+10√21)/(2116-2100)

46-10√21+(46+10√21)/16

46-10√21+2(23+5√21)/16

46-10√21+(23+5√21)/8

(368-80√21+23+5√21)/8

(345-75√21)/8

15(23-5√21)/8