Let $\alpha, \beta$ be the roots of the equation $x^2-x+2=0$ with $\operatorname{Im}(\alpha)>\operatorname{Im}(\beta)$. Then $\alpha^6+\alpha^4+\beta^4-5 \alpha^2$ is equal to ___________.
Answer (integer)
13
Solution
<p>$$\begin{aligned}
& \alpha^6+\alpha^4+\beta^4-5 \alpha^2 \\
& =\alpha^4(\alpha-2)+\alpha^4-5 \alpha^2+(\beta-2)^2 \\
& =\alpha^5-\alpha^4-5 \alpha^2+\beta^2-4 \beta+4 \\
& =\alpha^3(\alpha-2)-\alpha^4-5 \alpha^2+\beta-2-4 \beta+4 \\
& =-2 \alpha^3-5 \alpha^2-3 \beta+2 \\
& =-2 \alpha(\alpha-2)-5 \alpha^2-3 \beta+2 \\
& =-7 \alpha^2+4 \alpha-3 \beta+2 \\
& =-7(\alpha-2)+4 \alpha-3 \beta+2 \\
& =-3 \alpha-3 \beta+16=-3(1)+16=13
\end{aligned}$$</p>
About this question
Subject: Mathematics · Chapter: Complex Numbers and Quadratic Equations · Topic: Complex Numbers and Argand Plane
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