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Question

Find the value of x3+1/x3,if x2+1/x2=14

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Solution

x² + 1/x² = 14


(x + 1/x)² -2.x.1/x = 14

(x + 1/x )² -2 = 14

(x + 1/x )² = 16

take square root both sides

(x + 1/x) = 4

then,
[a³+b³=(a+b)³-3ab(a+b)]

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

= ( x +1/x)³ -3(x + 1/x)

= (4)³ -3(4)

= 64 - 12

= 52

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