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Algebra Level 1

x + 1 x = 2 x 6 + 1 x 6 = m \large x+\frac{1}{x}=2 \implies x^{6}+\frac{1}{x^{6}}=m

Solve for m m , where x x is a positive integer.


The answer is 2.

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4 solutions

Chew-Seong Cheong
Mar 30, 2018

x + 1 x = 2 Multiply throughout by x and rearrange. x 2 2 x + 1 = 0 ( x 1 ) 2 = 0 x = 1 \begin{aligned} x + \frac 1x & = 2 & \small \color{#3D99F6} \text{Multiply throughout by }x \text{ and rearrange.} \\ x^2 - 2x + 1 & = 0 \\ (x-1)^2 & = 0 \\ \implies x & = 1 \end{aligned}

Therefore, x 6 + 1 x 6 = 1 + 1 = 2 x^6 + \dfrac 1{x^6} = 1+1= \boxed{2}

Matin Naseri
Mar 30, 2018

x + \text{}x+ 1 x = a \frac{1}{x}=a \implies x 6 + \text{}x^{6}+ 1 x 6 = a 6 6 a 4 + 9 a 2 2 \frac{1}{x^{6}}={a^{6}}-{6{a^{4}}}+{9{a^{2}}}-2

we have :

x + \text{}x+ 1 x = 2 \frac{1}{x}=2 \implies x 6 + \text{}x^{6}+ 1 x 6 = m \frac{1}{x^{6}}=m

Solve for m \text{}m .

For x + \text{}x+ 1 x = 2 \frac{1}{x}=2 \implies x 6 + \text{}x^{6}+ 1 x 6 = 2 6 6 × 2 4 + 9 × 2 2 2 = 2 \frac{1}{x^{6}}= {2^{6}}-{6×{2^{4}}}+{9×{2^{2}}}-2 ={\boxed{2}}

Nicely done

A Former Brilliant Member - 3 years, 2 months ago
Ruồi Ăn Táo
Jul 27, 2018

x+1/x=2

(x+1/x)^2=4

x^2+1/x^2+2=4

x^2+1/x^2=2

(x^2+1/x^2)^3=8

x^6+1/x^6+3x1/x(x+1/x)=8

m+3*2=8

m=2

Munem Shahriar
Mar 31, 2018

x 6 + 1 x 6 = ( x 3 ) 2 + ( 1 x 3 ) 2 = ( x 3 + 1 x 3 ) 2 2 = { ( x + 1 x ) 3 3 ( x + 1 x ) } 2 2 = ( 2 3 3 × 2 ) 2 2 = ( 8 6 ) 2 2 = 2 2 2 = 4 2 = 2 . \begin{aligned} x^6 + \dfrac 1{x^6} & = (x^3)^2 + \left(\dfrac 1{x^3}\right)^2 \\ & = \left(x^3 + \dfrac 1{x^3} \right)^2 -2 \\ & = \left\{\left(x + \dfrac 1x \right)^3 - 3\left(x + \dfrac 1x \right)\right \}^2 -2 \\ & = (2^3 - 3 \times 2)^2 - 2 \\ & = (8 - 6)^2 -2 \\ & = 2^2 -2 \\ & = 4 - 2 \\ & = \boxed 2.\\ \end{aligned}

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