Question

If x^2+1/x^2=7.Find the value of x^3+1/x^3

Plz....Plz....Please answer it....Plz....

Answer 1

and try giving more points for questions otherwise no one will answer them....

Answer 2

Given x^2 + 1/x^2 = 7

= > x^2 + 1/x^2 + 2 = 9

It can be written as

= > x^2 + 1/x^2 + 2 * x^2 + 1/x^2 = 9

= > (x + 1/x)^2 = 9

= > x + 1/x = 3.


Now,

on cubing both sides, we get

(x + 1/x)^3 = (3)^3

x^3 + 1/x^3 + 3 * x * 1/x(x + 1/x) = 27

x^3 + 1/x^3 + 3(x + 1/x) = 27

x^3 + 1/x^3 + 3(3) = 27

x^3 + 1/x^3 + 9=27

 x^3 + 1/x^3 = 27 - 9

x^3 + 1/x^3 = 18


Hope this helps!