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Find the non-extraneous solutions of [tex]\sqrt{x+9}-5=x+4[/tex]

A. [tex]x=-9[/tex] and [tex]x=-8[/tex]
B. [tex]x=-2[/tex]
C. [tex]x=-9[/tex] and [tex]x=-2[/tex]
D. [tex]x=9[/tex]


Sagot :

Let's solve the equation [tex]\(\sqrt{x+9} - 5 = x + 4\)[/tex] to find its non-extraneous solutions. We'll go through the solution step-by-step.

1. Rewrite the equation:
[tex]\[ \sqrt{x + 9} - 5 = x + 4 \][/tex]

2. Isolate the square root:
[tex]\[ \sqrt{x + 9} = x + 9 \][/tex]

3. Square both sides to remove the square root:
[tex]\[ (\sqrt{x + 9})^2 = (x + 9)^2 \][/tex]
[tex]\[ x + 9 = (x + 9)^2 \][/tex]

4. Expand the right-hand side:
[tex]\[ x + 9 = x^2 + 18x + 81 \][/tex]

5. Bring all terms to one side of the equation to set it to zero:
[tex]\[ 0 = x^2 + 18x + 81 - x - 9 \][/tex]
[tex]\[ 0 = x^2 + 17x + 72 \][/tex]

6. Solve the quadratic equation using factorization:
[tex]\[ x^2 + 17x + 72 = 0 \][/tex]

Find factors of 72 that sum to 17:
[tex]\[ (x + 8)(x + 9) = 0 \][/tex]

Setting each factor equal to zero gives the potential solutions:
[tex]\[ x + 8 = 0 \quad \text{or} \quad x + 9 = 0 \][/tex]
[tex]\[ x = -8 \quad \text{or} \quad x = -9 \][/tex]

7. Verify each potential solution to check for extraneous solutions:

- For [tex]\(x = -8\)[/tex]:
[tex]\[ \sqrt{-8 + 9} - 5 \stackrel{?}{=} -8 + 4 \][/tex]
[tex]\[ \sqrt{1} - 5 = -4 \quad \text{True} \][/tex]

- For [tex]\(x = -9\)[/tex]:
[tex]\[ \sqrt{-9 + 9} - 5 \stackrel{?}{=} -9 + 4 \][/tex]
[tex]\[ \sqrt{0} - 5 = -5 \quad \text{True} \][/tex]

Thus, the non-extraneous solutions are [tex]\(x = -9\)[/tex] and [tex]\(x = -8\)[/tex].

Therefore, the correct answer is:
[tex]\[ (x = -9 \text{ and } x = -8) \][/tex]