Question

Solve if  x-1/x=7,find x31/x3

Answer 1

HEY!!

we know that ( a - b )3 = a3 + b3 - 3ab(a - b)

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

divide with x3

(x -1/x)3 =( x3 + 1)/x3 - 3x.7x/x3..........x-1=7x from problem

(7)3 = (x3 + 1)/x3 -21/x

343 + 21/x = x3 + 1/x3

Answer 2

Here is your answer 
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we know that ( a - b )3 = a3 + b3 - 3ab(a - b)


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


divide with x3

(x -1/x)3 =( x3 + 1)/x3 - 3x.7x/x3..........x-1=7x from problem


(7)3 = (x3 + 1)/x3 -21/x

343 + 21/x = x3 + 1/x3

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