I need help with number 40. Using substitution to factor a polynomial

Given the expression number 40:
[tex]x^2-x-1[/tex]we will use the substitution to factor the polynomial
To find the suitable substitution, find the factor which will be used to make a complete square, the factor will be = (coefficient of x/2)²
So, the factor will be =
[tex](-\frac{1}{2})^2=\frac{1}{4}[/tex]So, we will substitute:
[tex]\begin{gathered} u=x-\frac{1}{4} \\ so,x=u+\frac{1}{4} \end{gathered}[/tex]The substitution into the expression will be as follows:
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