I thought the completed square was the first part that was worked out.

x^2 - 8x - 5

(x - 4)^2 - 16 without the - 5 being added, why am I wrong?

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- Aug 9th 2011, 11:16 AMDavid GreenRe: Completing the square in quadratics of the form x^2 + bx + c
- Aug 9th 2011, 11:24 AMSironRe: Completing the square in quadratics of the form x^2 + bx + c
Completing the square is a technique for converting a quadratic polynomial of the form $\displaystyle ax^2+bx+c$ into the form $\displaystyle a(x-p)^2+q$ where $\displaystyle p,q$ are constants.

So that's what we've done here and notice $\displaystyle (x-4)^2-16=x^2-8x+16-16=x^2-8x$.

Does this answers your questions? ...

If you want to have a confirmation take a look here:

http://www.wolframalpha.com/input/?i=complete+the+square+of+x^2-8x-5