Question

If x^2+x =3^2/3+3^-2/3 then prove that 3x^3+9x-8=0

Answer 1

x^2 + 2 = 3^2/3 + 3^-2/3

x^2 = 3^2/3 + 3^-2/3 - 2

x = √(3^2/3 + 3^-2/3 - 2)

x = 0.748888296

Substitute for x in 3x^3 + 9x - 8:

3( 0.748888296)^3 + 9( 0.748888296) - 8 = 0.

So it is proved.