Just a Poly problem

Algebra Level 4

2 x 2 + 1 3 x 2 6 x + 9 = 1 x 2 6 x + 10 + 1 \large 2{ x }^{ 2 }+\frac { 1 }{ 3x^{ 2 }-6x+9 } =\frac { 1 }{ x^{ 2 }-6x+10 } +1

Find x > 0 x >0 that satisfies the equation above. Write your answer to 4 decimal places.


The answer is 0.7071.

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3 solutions

2 x 2 + 1 3 x 2 6 x + 9 = 1 x 2 6 x + 10 + 1 2 x 2 1 + 1 2 x 2 1 + x 2 6 x + 10 = 1 x 2 6 x + 10 Let a = 2 x 2 1 and b = x 2 6 x + 10 a + 1 a + b = 1 b a = 0 2 x 2 1 = 0 x = 1 2 0.7071 Since x > 0 \begin{aligned} 2x^2 + \frac 1{3x^2-6x+9} & = \frac 1{x^2-6x+10} + 1 \\ 2x^2 - 1 + \frac 1{2x^2 -1+x^2-6x+10} & = \frac 1{x^2-6x+10} & \small \color{#3D99F6} \text{Let }a = 2x^2-1 \text{ and }b = x^2-6x+10 \\ \implies a + \frac 1{a+b} & = \frac 1b \\ \implies a & = 0 \\ 2x^2 - 1 & = 0 \\ \implies x & = \frac 1{\sqrt 2} \approx \boxed {0.7071} & \small \color{#3D99F6} \text{Since }x > 0 \end{aligned}

Nice solution! Thanks!

Steven Jim - 4 years, 1 month ago

Third line a=0 is the solution. But a=2 * x * x - 1.
So x=0.707107.

Niranjan Khanderia - 2 years, 7 months ago

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Wow! You are right. I will change the solution.

Chew-Seong Cheong - 2 years, 7 months ago

L e t a = 2 x 2 , a n d b = x 2 6 x + 10. T h e n g i v e n e q u a t i o n i s : a + 1 / ( a + b 1 ) = 1 / b + 1. S e e e a s i l y a = 1 i s t h e s o l u t i o n . 2 x 2 = 1 , f o r x > 0 , x = 2 / 2 = 0.7071. Let~a=2x^2,~~and~~b=x^2-6x+10.\\ Then~given~equation~is:-\\ a+1/(a+b-1)=1/b+1.\\ See~easily~a=1~is~the~solution.\\ \implies~2x^2=1,~~for~x>0, ~~x=\sqrt2/2=0.7071.

Vilakshan Gupta
Mar 9, 2018

If you try to compare L.H.S and R.H.S, we simply see that x = 1 2 x=\dfrac{1}{\sqrt{2}}

First set 2 x 2 = 1 2x^2=1 , which which will give you x = 1 2 x=\dfrac{1}{\sqrt{2}} (not a negative result because it's not allowed) and then set 1 3 x 2 6 x + 9 = 1 x 2 6 x + 10 \dfrac { 1 }{ 3x^{ 2 }-6x+9 }=\dfrac { 1 }{ x^{ 2 }-6x+10 } , which again gives you x = 1 2 0.7071 x=\boxed{\dfrac{1}{\sqrt{2}}\approx 0.7071} , hence it satisfies!


Although It's not a solution...

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