Irrational Equation

Algebra Level 4

What is the sum of all the x x 's that satisfy the equation below? x 2 x 10 x 2 x 11 = 22 x^2-x-10 \sqrt{x^2-x-11}=22

1 4 3 2

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.

3 solutions

Chew-Seong Cheong
Oct 19, 2015

x 2 x 10 x 2 x 11 = 22 x 2 x 11 + 11 10 x 2 x 11 = 22 Let y 2 = x 2 x 11 y 2 + 11 10 y = 22 y 2 10 y 11 = 0 ( y + 1 ) ( y 11 ) = 0 y = { 1 Rejected since x 2 x 11 0 11 Accepted x 2 x 11 = 1 1 2 x 2 x 132 = 0 \begin{aligned} x^2 - x - 10 \sqrt{x^2 -x - 11} & = 22 \\ \color{#3D99F6}{x^2 - x - 11} + 11 - 10 \sqrt{\color{#3D99F6}{x^2 - x - 11}} & = 22 \quad \quad \small \color{#3D99F6}{\text{Let } y^2 = x^2 - x - 11} \\ y^2 + 11 - 10y & = 22 \\ y^2 -10y - 11 & = 0 \\ (y+1)(y-11) & = 0 \\ \Rightarrow y & = \begin{cases} - 1 & \color{#D61F06}{\text{Rejected since } \sqrt{x^2 - x - 11} \ge 0} \\ 11 & \color{#3D99F6}{\text{Accepted}} \end{cases} \\ \Rightarrow x^2 - x - 11 & = 11^2 \\ x^2 - x - 132 & = 0 \end{aligned}

By Vieta's formulas, the sum of roots of x x is 1 \boxed{1} .

Why would you reject y = -1, since y = -1 Comes out to be x2-x-12 = 0

Rik Sen - 5 years, 7 months ago

Log in to reply

y = x 2 x 11 y = x^2-x-11 , when y = 1 y=-1 , x 2 x 11 = 1 \sqrt{x^2-x-11} = \sqrt{-1} is not real.

Chew-Seong Cheong - 2 years, 11 months ago
Somnath Singh
Mar 24, 2014

Consider x^2 -x-11 = A , Substituting the A in the Given Equation we get :-

New Equation :- A^2 -10A + 11=0 The value of A would be { (10 + Sqrt(56))/2 , (10 - Sqrt(56))/2) } = Real Number Let's say 'N'.

Putting the Value of A we get :-

Now x^2 -x-11 = N => x^2 -x -(11+N) =0

The Summation of Roots is -b/a for a Equation ax^2 + bx + c = 0..

So the sum of the Roots of x is [ - ( -1) / 1] = 1 (Ans)

Nguyen Trung
Mar 18, 2014

equaltion:

x^{2} -x-11 -10*\sqrt(x^{2} -x-11) + 5^{2}=36

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...