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Algebra Level 3

Is x = 37 x = 37 the only (not necessarily real) value for x x which satisfies the following equation: x 3 x 2 x = 3 7 3 3 7 2 37 x^3 - x^2 - x = 37^3 - 37^2 - 37 ?

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1 solution

Munem Shahriar
Sep 15, 2018

x 3 x 2 x = 3 7 3 3 7 2 37 x 3 x 2 x 49247 = 0 x^3 - x^2 - x = 37^3 - 37^2 - 37 \implies x^3 - x^2 - x - 49247 = 0 . Assume f ( x ) = x 3 x 2 x 49247 f(x) = x^3 - x^2 - x - 49247

x 3 x 2 x 49247 = 0 x 3 37 x 2 + 36 x 2 1332 x + 1331 x 49247 = 0 x 2 ( x 37 ) + 36 x ( x 37 ) + 1331 ( x 37 ) = 0 ( x 37 ) ( x 2 + 36 x + 1331 ) = 0 x 2 + 36 x + 1331 = 0 \begin{aligned} x^3 - x^2 - x - 49247& = 0 \\ \Rightarrow x^3 - 37x^2 + 36x^2 -1332x+1331x-49247 & = 0 \\ \Rightarrow x^2(x - 37) + 36x(x -37) +1331(x-37) & = 0 \\ \Rightarrow (x - 37)(x^2 + 36 x + 1331) & = 0 \\ \Rightarrow x^2 + 36x + 1331 & = 0 \\ \end{aligned}

By the quadratic equation formula, we get x = 18 ± i 1007 x = -18 \pm i\sqrt{1007} . Hence x = 37 x = 37 is not unique.

Note: x 37 x - 37 is a factor of f ( x ) f(x) because f ( 37 ) = 0 f(37) =0

You can add a link of the factor theorem;

Syed Hamza Khalid - 2 years, 8 months ago

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