<s>[INST] What's $\alpha+\beta$ if we have: $\alpha^3-6\alpha^2+13\alpha=1$ and $\beta^3-6\beta^2+13\beta=19$ ($\alpha$ and $\beta$ are Real) What's $\alpha+\beta$ if we have $\alpha^3-6\alpha^2+13\alpha=1$ and $\beta^3-6\beta^2+13\beta=19$? Here $\alpha$ and $\beta$ are real. 
Firstly, I subtracted the two equations and got the following:
$$\alpha^3-\beta^3-6(\alpha^2-\beta^2)+13(\alpha-\beta)=-18$$ Then I tried to factorize the left hand side as: $$(\alpha-\beta)(\alpha^2+\alpha\beta+\beta^2-6\alpha-6\beta+13)=-18$$ 
At this point it seems we can't go on!
Then I tried adding the two equations as: $$(\alpha+\beta)(\alpha^2-\alpha\beta+\beta^2-6\alpha-6\beta+13)+12\alpha\beta=20$$
unfortunately, again I can't continue!
Is there any special creativity needed for solving this question?
 [/INST] Let $f(x)=x^3-6x^2+13x,$ Then $f'(x)=3x^2-12x+13 = 3[(x-2)^2]+1>0$
So $f(x)$ is strictly increasing function.
Now above we have given $f(\alpha)=1$ and $f(\beta) = 19\;,$ Where $\alpha<\beta$
Then $f(\alpha)<f(\beta)$, because the function is increasing.
Now \begin{align*}f(4-x)&=(4-x)^3-6(4-x)^2+13(4-x)\\&=64-x^3-48x+12x^2-96-6x^2+48x+52-13x\\&=-x^3+6x^2-13x+20=-f(x)+20\end{align*}
So if $x=\alpha$, Then $f(4-\alpha)=-f(\alpha)+20=19=f(\beta)$
The function is continuous and monotonically increasing, thus $f(x)=f(y)\implies x=y$, hence $$4-\alpha=\beta\Rightarrow \boxed{\alpha+\beta=4}$$
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