Transforming x^5-x^4-x^3-x^2-x-1 to y^5+2y^2+47y+122

[footmath]

Hello , please guide me .
How can I transformed the equation $$x^{5}-x^{4}-x^{3}-x^{2}-x-1 =0$$to $$y^{5}+2y^{2}+47y+122$$ ?
I studied a lecture that the writer had written :<< by using $$y=x^{2}-3x$$ we can transformed $$x^{5}-x^{4}-x^{3}-x^{2}-x-1 =0$$ to $$y^{5}+2y^{2}+47y+122$$ But how ? if in $$y=x^2-3x$$ we obtain $$x$$ by $$y$$ we will have : $$x=3/2+\sqrt{y+9/4}$$ and if we substitute $$x=3/2+\sqrt{y+9/4}$$ in $$x^{5}-x^{4}-x^{3}-x^{2}-x-1 =0$$ we don't have $y^5+2y^2+47y+122$ . please explain it.
Thank you very much

 

[Mark44]

footmath, please edit your post to fix your LaTeX. All of your TEX and /TEX tags need to be written in lower case - as tex and /tex (inside square brackets).