Question

$8x^3-6x-1=0$

Answer 1

сделаем замену 

$x=cosx\ 8cos^3x-6cosx-1=0\ cosx(8cos^2x-6cosx)-1=0\ 2cos3x-1=0\ 2cos3x=1\ x=frac{pi}{9}\ x=cos(frac{pi}{9}})=0.939\ vtoroy koren' posle delenia nawego vyrazhenia na cos(frac{pi}{9}})$\

teper'\ zamena \ na \ x=sinx\

$teper'\ zamena \ na \ x=sinx$

8sin^3x-6sinx-1=0
-2sin3x-1=0
x=-pi/18+pi*k/2
sin(-pi/18)=-0.17...
sin(-5pi/18)=-0.766....