How do you solve (5-x)^(1/2) = x + 1 and find any extraneous solutions?

2 Answers
Aug 28, 2017

See a solution process below:

Explanation:

First, we can square both sides of the equation to eliminate the fractional exponent while keeping the equation balanced:

((5 - x)^(1/2))^2 = (x + 1)^2

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

5 - x = x^2 + 2x + 1

Next, we can convert the equation into standard form:

5 - x - color(red)(5) + color(blue)(x) = x^2 + 2x + 1 - color(red)(5) + color(blue)(x)

5 - color(red)(5) - x + color(blue)(x) = x^2 + 2x + color(blue)(x) + 1 - color(red)(5)

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

0 = x^2 + 3x - 4

x^2 + 3x - 4 = 0

Now, we can use the quadratic equation to solve this problem:

The quadratic formula states:

For color(red)(a)x^2 + color(blue)(b)x + color(green)(c) = 0, the values of x which are the solutions to the equation are given by:

x = (-color(blue)(b) +- sqrt(color(blue)(b)^2 - (4color(red)(a)color(green)(c))))/(2 * color(red)(a))

Substituting:

color(red)(1) for color(red)(a)

color(blue)(3) for color(blue)(b)

color(green)(-4) for color(green)(c) gives:

x = (-color(blue)(3) +- sqrt(color(blue)(3)^2 - (4 * color(red)(1) * color(green)(-4))))/(2 * color(red)(1))

x = (-color(blue)(3) +- sqrt(9 - (-16)))/2

x = (-color(blue)(3) - sqrt(9 - (-16)))/2 and x = (-color(blue)(3) + sqrt(9 - (-16)))/2

x = (-color(blue)(3) - sqrt(9 + 16))/2 and x = (-color(blue)(3) + sqrt(9 + 16))/2

x = (-color(blue)(3) - sqrt(25))/2 and x = (-color(blue)(3) + sqrt(25))/2

x = (-color(blue)(3) - 5)/2 and x = (-color(blue)(3) + 5)/2

x = -8/2 and x = 2/2

x = -4 and x = 1

Substituting both solutions into the original equation gives:

(5 - (-4))^(1/2) = -4 + 1 and (5 - 1)^(1/2) = 1 + 1

(5 + 4)^(1/2) = -3 and (4)^(1/2) = 2

(9)^(1/2) = -3 and 2 = 2

3 != -3 and 2 = 2

Therefore the solution x = -4 is extraneous.

Aug 28, 2017

color(magenta)(x=1 or x=-4

Explanation:

(5-x)^(1/2)=x+1

:.sqrt(5-x)=x+1

square both sides

:.(sqrt(5-x))^2=(x+1)^2

:.5-x=x^2+2x+1

:.x^2+2x+1=5-x

:.x^2+2x+x+1-5=0

:.x^2+3x-4=0

:.(x-1)(x+4)=0

:.color(magenta)(x=1 or x=-4