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What is the solution of the equation [tex]\((x-5)^2 + 3(x-5) + 9 = 0\)[/tex]? Use [tex]\(u\)[/tex] substitution and the quadratic formula to solve.

A. [tex]\(x = \frac{-3 \pm 3i\sqrt{3}}{2}\)[/tex]

B. [tex]\(x = \frac{7 \pm 3i\sqrt{3}}{2}\)[/tex]

C. [tex]\(x = 2\)[/tex]

D. [tex]\(x = 8\)[/tex]

Sagot :

To solve the equation [tex]\((x-5)^2 + 3(x-5) + 9 = 0\)[/tex], we can use a substitution method. Let's follow the steps in detail:

1. Substitute:
Let [tex]\( u = x - 5 \)[/tex]. Then, our equation becomes:
[tex]\[ u^2 + 3u + 9 = 0 \][/tex]

2. Quadratic formula:
Now we need to solve the quadratic equation [tex]\( u^2 + 3u + 9 = 0 \)[/tex] using the quadratic formula [tex]\( u = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \)[/tex].
Here,
[tex]\( a = 1 \)[/tex],
[tex]\( b = 3 \)[/tex],
[tex]\( c = 9 \)[/tex].

3. Calculate the discriminant:
The discriminant [tex]\(\Delta\)[/tex] is given by:
[tex]\[ \Delta = b^2 - 4ac \][/tex]
Substitute [tex]\(a\)[/tex], [tex]\(b\)[/tex], and [tex]\(c\)[/tex] into the discriminant formula:
[tex]\[ \Delta = 3^2 - 4 \cdot 1 \cdot 9 = 9 - 36 = -27 \][/tex]

4. Solve for [tex]\( u \)[/tex] :
Since the discriminant is negative ([tex]\(\Delta = -27\)[/tex]), the solutions will be complex. We proceed with finding the roots using the quadratic formula:
[tex]\[ u = \frac{-b \pm \sqrt{\Delta}}{2a} \][/tex]
Substitute [tex]\( b = 3 \)[/tex], [tex]\( \Delta = -27 \)[/tex], and [tex]\( a = 1 \)[/tex]:
[tex]\[ u = \frac{-3 \pm \sqrt{-27}}{2 \cdot 1} = \frac{-3 \pm \sqrt{-27}}{2} \][/tex]
Rewrite [tex]\(\sqrt{-27}\)[/tex] as [tex]\(\sqrt{27i^2} = i\sqrt{27} = 3i\sqrt{3}\)[/tex]:
[tex]\[ u = \frac{-3 \pm 3i\sqrt{3}}{2} \][/tex]
So, the solutions for [tex]\( u \)[/tex] are:
[tex]\[ u_1 = \frac{-3 + 3i\sqrt{3}}{2} \][/tex]
[tex]\[ u_2 = \frac{-3 - 3i\sqrt{3}}{2} \][/tex]

5. Substitute back:
Recall that [tex]\( u = x - 5 \)[/tex]. Therefore,
[tex]\[ x - 5 = \frac{-3 + 3i\sqrt{3}}{2} \][/tex]
[tex]\[ x - 5 = \frac{-3 - 3i\sqrt{3}}{2} \][/tex]

6. Solve for [tex]\( x \)[/tex]:
Add 5 to both equations to solve for [tex]\( x \)[/tex]:
[tex]\[ x_1 = 5 + \frac{-3 + 3i\sqrt{3}}{2} = \frac{10 - 3 + 3i\sqrt{3}}{2} = \frac{7 + 3i\sqrt{3}}{2} \][/tex]
[tex]\[ x_2 = 5 + \frac{-3 - 3i\sqrt{3}}{2} = \frac{10 - 3 - 3i\sqrt{3}}{2} = \frac{7 - 3i\sqrt{3}}{2} \][/tex]

Thus, the solutions to the equation [tex]\((x-5)^2 + 3(x-5) + 9 = 0\)[/tex] are:
[tex]\[ \boxed{x = \frac{7 + 3i\sqrt{3}}{2} \quad \text{and} \quad x = \frac{7 - 3i\sqrt{3}}{2}} \][/tex]

These match the second option from the given list of possible solutions.