Consider The Reciprocal First!

Algebra Level 1

If x + 1 x = 3 , then find the value of x 1 + x + x 2 . \text{ If } x + \dfrac1x = 3, \text{ then find the value of } \dfrac x{1+x+x^2}.

5 4 \frac{5}{4} 1 4 \frac{1}{4} 1 3 \frac{1}{3} 3 4 \frac{3}{4}

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.

7 solutions

Kennedy Nguyen
Nov 8, 2015

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

Dividing numerator and denominator by x and noting that x 0 \neq 0 ,

= 1 1 x + 1 + x = \frac{1}{ \frac{1}{x} + 1 + x}

= 1 3 + 1 = \frac{1}{3+1}

= 1 4 = \frac{1}{4}

Jack Rawlin
Nov 10, 2015

By re-arranging the first formula we get

x 2 + 1 = 3 x x^2 + 1 = 3x

If we add x x to that we get

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

That's the same as the bottom of the second equation, this means we can substitute it in

x 1 + x + x 2 x 4 x \frac{x}{1 + x + x^2} \Rightarrow \frac{x}{4x}

Cancelling the x x 's gives us

x 4 x = 1 4 \frac{x}{4x} = \boxed{\frac{1}{4}}

x 1 + x + x 2 = ( 1 + x + x 2 x ) 1 = ( 1 x + 1 + x ) 1 = ( 1 + 3 ) 1 = 4 1 = 1 4 \frac {x}{1+x+x^2} = \left(\frac{1+x+x^2}{x}\right)^{-1} = \left(\frac{1}{x} + 1 + x\right)^{-1} = (1+3)^{-1} = 4^{-1} = \frac{1}{4}

Prasit Sarapee
Nov 10, 2015

x+1/x=3
---> x^2+1=3x
--->x^2+x+1=4x
--->(x^2+x+1)/x=4
--->x/(x^2+x+1)=1/4



Fahim Faisal
Nov 10, 2015

multiply out by x. so, x 2 + 1 = 3 x x^{2} + 1 = 3x . now add x. so, we now have, x 2 + x + 1 = 4 x x^{2} +x + 1=4x .

x/ [ 1 + x + x 2 ] [1+x+x^{2}] = x/4x = 1/4

Harish Nani
Nov 8, 2015

x+1/x=3 by solving it we get thatx^2+1=3x by substituitindsubstituiting in given equation we get answer is 1/4

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...