Question

If X^2+ 1/X^2 =7 , find the value of X ^3+1/X ^3....

Answer 1

Assume and try (x + 1/x)2 = x2 + 1/x2 + 2

(x + 1/x)2 = 9

x + 1/x = 3

 

now

(x + 1/x)3 = x3 + 1/x3 + 3(x + 1/x)

27 = x3 + 1/x3 + 9

or

x3 + 1/x3 = 27 - 9 =  18

it shoul be the answer