x 2 + 1 x 2 x^2+\frac{1}{x^2}

Algebra Level 2

If x 2 13 x + 1 = 0 , x^2-13x+1=0, what is the value of x 2 + 1 x 2 ? x^2+\frac{1}{x^2}?

167 173 171 169

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

4 solutions

Anish Puthuraya
Feb 26, 2014

x 2 + 1 x 2 = ( x + 1 x ) 2 2 x^2+\frac{1}{x^2} = \left(x+\frac{1}{x}\right)^2-2 x 2 + 1 x 2 = ( x 2 + 1 x ) 2 2 x^2+\frac{1}{x^2} = \left(\frac{x^2+1}{x}\right)^2-2

From the given quadratic,
x 2 + 1 = 13 x x^2+1 = 13x

Thus,
x 2 + 1 x 2 = ( 13 x x ) 2 2 = 167 x^2+\frac{1}{x^2} = \left(\frac{13x}{x}\right)^2 -2 = \boxed{167}

May you show step by step the solution.

Vinicius Beserra - 7 years, 3 months ago

167

Namrita Triar - 7 years, 3 months ago

167 because let us take a and b as its roots so, a+b=13 &a*b=1 therefore, b+(1/b)=13 and x^2+1/(x^2)=(x+(1/x))^2-2 and b is one of roots so (b+(1/b))^2-2=167 .

Prafull Sharma - 7 years, 3 months ago
Shreyas Shastry
Feb 27, 2014

x^2-13x+1=0 x^2+1=13x x^2+1/x=13 after simplification we get x+1/x=13 and on squaring both the sides we get x^2+1/x^2=167

thnx

raima rashid - 7 years, 3 months ago
Victor Loh
Mar 17, 2014

Note that

x 2 + 1 x 2 = ( x + 1 x ) 2 2 x^{2}+\frac{1}{x^{2}}=(x+\frac{1}{x})^{2}-2

Hence all we have to do is to find x + 1 x x+\frac{1}{x} .

Since x x is not equal to 0 0 , we can divide both sides of x 2 13 x + 1 = 0 x^{2}-13x+1=0 by x x , we have

x 13 + 1 x = 0 x + 1 x = 13 x-13+\frac{1}{x}=0 \implies x+\frac{1}{x}=13

Therefore, the desired answer is 1 3 2 2 = 167 13^{2}-2=\boxed{167} , and we are done.

Yash Shukla
Mar 2, 2014

on looking at eqn , product of roots is 1.. so we can assume it as x & 1/x, also x+1/x=13, put in formula of (x+1/x)^2=x^2+1/x^2 + 2, we get directly the answer...167

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...