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Solve the radical equation.
[tex]\[ x + 1 = \sqrt{-6x - 6} \][/tex]

Which solution is extraneous?
A. The solution [tex]\( x = -1 \)[/tex] is an extraneous solution.
B. Both [tex]\( x = 1 \)[/tex] and [tex]\( x = 7 \)[/tex] are true solutions.
C. The solution [tex]\( x = 7 \)[/tex] is an extraneous solution.
D. Neither [tex]\( x = 1 \)[/tex] nor [tex]\( x = 7 \)[/tex] is a true solution to the equation.


Sagot :

To solve the given radical equation:

[tex]\[ x + 1 = \sqrt{-6x - 6} \][/tex]

we need to follow several steps methodically to find the solutions and check for any extraneous ones.

### Step-by-Step Solution

1. Isolate the Radical Expression:
[tex]\[ x + 1 = \sqrt{-6x - 6} \][/tex]

2. Square Both Sides to eliminate the square root. This gives:
[tex]\[ (x + 1)^2 = (\sqrt{-6x - 6})^2 \][/tex]

Simplifying, we get:
[tex]\[ (x + 1)^2 = -6x - 6 \][/tex]

3. Expand the Left Side:
[tex]\[ x^2 + 2x + 1 = -6x - 6 \][/tex]

4. Move All Terms to One Side to set the equation to zero:
[tex]\[ x^2 + 2x + 1 + 6x + 6 = 0 \][/tex]

Simplifying further:
[tex]\[ x^2 + 8x + 7 = 0 \][/tex]

5. Solve the Quadratic Equation using the quadratic formula [tex]\(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\)[/tex] where [tex]\(a = 1\)[/tex], [tex]\(b = 8\)[/tex], and [tex]\(c = 7\)[/tex]:

[tex]\[ x = \frac{-8 \pm \sqrt{8^2 - 4 \cdot 1 \cdot 7}}{2 \cdot 1} \][/tex]

[tex]\[ x = \frac{-8 \pm \sqrt{64 - 28}}{2} \][/tex]

[tex]\[ x = \frac{-8 \pm \sqrt{36}}{2} \][/tex]

[tex]\[ x = \frac{-8 \pm 6}{2} \][/tex]

This gives two solutions:
[tex]\[ x = \frac{-8 + 6}{2} = \frac{-2}{2} = -1 \][/tex]
[tex]\[ x = \frac{-8 - 6}{2} = \frac{-14}{2} = -7 \][/tex]

6. Check Each Solution for Extraneous Solutions by substituting them back into the original equation [tex]\(x + 1 = \sqrt{-6x - 6}\)[/tex]:

- For [tex]\(x = -1\)[/tex]:
[tex]\[ -1 + 1 = \sqrt{-6(-1) - 6} \][/tex]
[tex]\[ 0 = \sqrt{6 - 6} \][/tex]
[tex]\[ 0 = \sqrt{0} \][/tex]
[tex]\[ 0 = 0 \, \text{(True)} \][/tex]
Hence, [tex]\(x = -1\)[/tex] is a valid solution.

- For [tex]\(x = -7\)[/tex]:
[tex]\[ -7 + 1 = \sqrt{-6(-7) - 6} \][/tex]
[tex]\[ -6 = \sqrt{42 - 6} \][/tex]
[tex]\[ -6 = \sqrt{36} \][/tex]
[tex]\[ -6 \neq 6 \, \text{(False)} \][/tex]
Hence, [tex]\(x = -7\)[/tex] is an extraneous solution.

### Conclusion

The solution [tex]\(x = -1\)[/tex] is a true solution to the equation [tex]\(x + 1 = \sqrt{-6x - 6}\)[/tex]. The solution [tex]\(x = -7\)[/tex] is an extraneous solution. Therefore:

- The solution [tex]\(x = -1\)[/tex] is not an extraneous solution.
- The solution [tex]\(x = -7\)[/tex] is an extraneous solution.

So the correct statement is:

- The solution [tex]\(x = -7\)[/tex] is an extraneous solution.
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