Thursday, January 22, 2015

Solve the equation x=1+square root(1+square root x).

First, we'll impose the constraint of existence of square
root;


x>=0


1 +
sqrtx>=0


We'll subtract 1 both
sides:


x - 1 = sqrt[1 +
sqrt(x)]


We'll raise to square both sides, to eliminate the
square root from the right side:


(x-1)^2 = 1 + sqrt
x


We'll expand the square:


x^2
- 2x + 1 = 1 + sqrtx


We'll eliminate like
terms:


x^2 - 2x = sqrt x


We'll
raise to square:


(x^2 - 2x)^2 =
x


[x(x - 2)]^2 - x = 0


We'll
factorize by x:


x[x(x-2)^2 - 1] =
0


x1 = 0


x(x-2)^2 - 1 =
0


We'll expand the square:


x^3
- 4x^2 + 4x - 1 = 0


We'll factorize the middle terms by
-4x:


(x^3 - 1) - 4x(x - 1) =
0


We'll re-write the difference of
cubes;


x^3 - 1 = (x - 1)(x^2 + x +
1)


(x - 1)(x^2 + x + 1) - 4x(x - 1) =
0


We'll factorize by
(x-1):


(x-1)(x^2 + x + 1 - 4x) =
0


x - 1 = 0


x2 =
1


x^2 - 3x + 1 = 0


We'll apply
the quadratic formula:


x3 = [3+sqrt(9 -
4)]/2


x3 = (3 + sqrt5)/2


x4 =
(3 - sqrt5)/2


The solutions of the equation
are: {0 ; (3 - sqrt5)/2 ; 1 ; (3 + sqrt5)/2}.

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