Answer:
18
Step-by-step explanation:
x^2 + 1/x^2 = 7
taking add 2 on both sides
x^2 + 1/x^2 +2 = 7 + 2
(x + 1/x)^2 = 9
(x + 1/x)^2 = 3^2
(x + 1/x) = 3
taking cube on both sides
(x + 1/x)^3 = 3^3
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