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Algebra Difficulty 5.0 AIME Prove it Nordic Mathematical Olympiad

Problem:
Determine the number of real roots of the equation
x8x7+2x62x5+3x43x3+4x24x+52=0 x^{8}-x^{7}+2 x^{6}-2 x^{5}+3 x^{4}-3 x^{3}+4 x^{2}-4 x+\frac{5}{2}=0

Solution

Solution:
Write
x8x7+2x62x5+3x43x3+4x24x+52=x(x1)(x6+2x4+3x2+4)+52 \begin{gathered} x^{8}-x^{7}+2 x^{6}-2 x^{5}+3 x^{4}-3 x^{3}+4 x^{2}-4 x+\frac{5}{2} \\ =x(x-1)\left(x^{6}+2 x^{4}+3 x^{2}+4\right)+\frac{5}{2} \end{gathered}
If x(x1)0x(x-1) \geq 0, i.e. x0x \leq 0 or x1x \geq 1, the equation has no roots. If 0<x<10<x<1, then 0>x(x1)=(x12)214140>x(x-1)=\left(x-\frac{1}{2}\right)^{2}-\frac{1}{4} \geq-\frac{1}{4} and x6+2x4+3x+4<1+2+3+4=10x^{6}+2 x^{4}+3 x+4<1+2+3+4=10. The value of the left-hand side of the equation now is larger than 1410+52=0-\frac{1}{4} \cdot 10+\frac{5}{2}=0. The equation has no roots in the interval (0,1)(0,1) either.

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