If x2 +-= 27, find the value of. x3 – InterviewSolution

1.

If x2 +-= 27, find the value of. x3

Answer»

X² + 1/x² = 27

(x + 1/x)² -2.x.1/x = 27

(x + 1/x )² -2 = 27

(x + 1/x )² = 25

take square root both sides

(x + 1/x) = 5

then,

x³ + 1/x³ = ( x + 1/x)³ - 3.x.1/x(x + 1/x)

= ( x +1/x)³ - 3(x + 1/x)

= (5)³ - 3(5)

= 125 - 15

= 110

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