Question

1
6.
If x3 +1/x3
= 198 then find the value of x +1/x

1) 5.5
2) 6
3) 6.25
4) 7​

Answer 1

Answer:

,a^3 + b^3 = [a + b]^3 -3*(a^2)*b -3*a*(b^2)

This will give us x^3 + (1/x)^3 = [x + 1/x]^3 -3*x -3*(1/x)

this implies 198 = [x + 1/x]^3 - 3* [x + 1/x]

by taking [x + 1/x] as 'p' we can see its a quadratic equation.

So by solving p^3 -3*p -198 = 0, we will get p=6 and -3 + 4.898i

[where i =(-1)^0.5]

So if you take the REAL value