Saturday, January 24, 2015

Solve the equation (x^3 - x)^1/2 + (2x - 1)^1/2 = (x^3 + x - 1)1/2.

To solve the equation and to eliminate the square
roots, we'll square raise both sides:


[sqrt(x^3 - x) +
sqrt(2x - 1)]^2= [sqrt(x^3 + x - 1)]^2


x^3 - x + 2x - 1 +
2sqrt[(x^3 - x)(2x - 1)] = x^3 + x - 1


We'll combine and
eliminate like terms and we'll get:


2sqrt[(x^3 - x)(2x -
1)] = 0


We'll divide by
2:


[(x^3 - x)(2x - 1)] =
0


We'll set each factor as
zero:


x^3 - x = 0


We'll
factorize:


x(x^2-1) = 0


We'll
expand the difference of squares:


x(x-1)(x+1) =
0


We'll set each factor as
zero:


x1 = 0


x-1 =
0


x2 = 1


x+1 =
0


x3 = -1


2x - 1 =
0


2x = 1


x4 =
1/2


Now, we'll check the found results in
equation:


For x1 = 0


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


sqrt(0) + sqrt( -
1)= sqrt( - 1)


But sqrt -1 is
impossible!


For x2 = 1


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


0 + 1 =
1


1=1


So x = 1
is admissible.


For x3 =
-1


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


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


sqrt -3 = sqrt-3


But,
sqrt-3 is impossible!


For x =
1/2


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


sqrt(1/8- 1/2) + sqrt(2/2 - 1)= sqrt(1/8 +1/2 -
1)


But sqrt -3/8 is
impossible!


So, the only admissible solution
of the equation is x = 1.

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