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Algebra Level 1

If x 2 11 x + 1 = 0 , \large x^{2}-11x+1=0, then find x + 1 x . \large x+\frac{1}{x}.


The answer is 11.

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7 solutions

Clearly x 0 , x \ne 0, so upon dividing through by x x the equation becomes

x 11 + 1 x = 0 x + 1 x = 11 . x - 11 + \dfrac{1}{x} = 0 \Longrightarrow x + \dfrac{1}{x} = \boxed{11}.

Sahil Sharma
Oct 29, 2015

We can see that the product of the roots of the given equation is 1. Which means roots are reciprocal of each other I.e x & 1/x. So what is asked is nothing but the sum of the roots which is clearly 11.

Saiful Haque
Oct 31, 2015

firstly x^2+1=11x or,x+1/x=11

Michael Fuller
Oct 31, 2015

x ( x 11 ) + 1 = 0 x 11 = 1 x 11 = ( x + 1 x ) x + 1 x = 11 x(x-11)+1=0 \\ x-11=-\frac{1}{x} \\ -11=-(x+ \frac{1}{x}) \\ x+ \frac{1}{x}= \large \color{#20A900}{\boxed{11}}

Chandresh Shah
Oct 30, 2015

x^2 - 11x +1 =0

x^2 + 1 = 11X hence divide both side by X we get X+1/X=11. Simple.

Bot Villegas
Oct 30, 2015

x^2 - 11x +1 =0

x^2 + 1 = 11x

x+1/x =11 therefore: x+1/x =11

Atika Samiha
Oct 29, 2015

x(x-11+1/x)=0 or,x-11+1/x=0,as x not equal to 0 so,(x+1/x)=11.

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