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Use the quadratic formula to determine the roots for the following equation:

[tex]\[ 2x^2 - 10x + 17 = 0 \][/tex]

A. [tex]\( x = \frac{5 \pm 3i}{2} \)[/tex]

B. [tex]\( x = 2, x = 8 \)[/tex]

C. [tex]\( x = \frac{-5 \pm 3i}{2} \)[/tex]

D. [tex]\( x = -2, x = -8 \)[/tex]


Sagot :

Let's solve the quadratic equation [tex]\(2x^2 - 10x + 17 = 0\)[/tex] using the quadratic formula.

The quadratic formula is:

[tex]\[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \][/tex]

For the given equation [tex]\(2x^2 - 10x + 17 = 0\)[/tex], the coefficients are:
- [tex]\(a = 2\)[/tex]
- [tex]\(b = -10\)[/tex]
- [tex]\(c = 17\)[/tex]

### Step 1: Calculate the Discriminant
The discriminant ([tex]\(\Delta\)[/tex]) is calculated using the formula:

[tex]\[ \Delta = b^2 - 4ac \][/tex]

Plug in the values of [tex]\(a\)[/tex], [tex]\(b\)[/tex], and [tex]\(c\)[/tex]:

[tex]\[ \Delta = (-10)^2 - 4 \cdot 2 \cdot 17 \][/tex]

[tex]\[ \Delta = 100 - 136 \][/tex]

[tex]\[ \Delta = -36 \][/tex]

Since the discriminant is negative ([tex]\(\Delta = -36\)[/tex]), the roots of the equation will be complex (i.e., they will involve imaginary numbers).

### Step 2: Calculate the Real and Imaginary Parts of the Roots
First, calculate the real part of the roots, which is shared by both roots:

[tex]\[ \text{Real part} = \frac{-b}{2a} \][/tex]

Plug in the values:

[tex]\[ \text{Real part} = \frac{-(-10)}{2 \cdot 2} \][/tex]

[tex]\[ \text{Real part} = \frac{10}{4} \][/tex]

[tex]\[ \text{Real part} = 2.5 \][/tex]

Next, calculate the imaginary part. The imaginary part is given by:

[tex]\[ \text{Imaginary part} = \frac{\sqrt{|\Delta|}}{2a} \][/tex]

Since [tex]\(\Delta\)[/tex] is negative, we take the absolute value of [tex]\(\Delta\)[/tex] for the imaginary part calculation:

[tex]\[ |\Delta| = 36 \][/tex]

[tex]\[ \text{Imaginary part} = \frac{\sqrt{36}}{2 \cdot 2} \][/tex]

[tex]\[ \text{Imaginary part} = \frac{6}{4} \][/tex]

[tex]\[ \text{Imaginary part} = 1.5 \][/tex]

### Step 3: Write the Roots
Using the real and imaginary parts, the roots of the quadratic equation are:

[tex]\[ x_1 = \text{Real part} + \text{Imaginary part} \cdot i \][/tex]

[tex]\[ x_2 = \text{Real part} - \text{Imaginary part} \cdot i \][/tex]

Substituting the values:

[tex]\[ x_1 = 2.5 + 1.5i \][/tex]

[tex]\[ x_2 = 2.5 - 1.5i \][/tex]

Hence, the roots of the quadratic equation [tex]\(2x^2 - 10x + 17 = 0\)[/tex] are:

[tex]\[ x = 2.5 + 1.5i \quad \text{and} \quad x = 2.5 - 1.5i \][/tex]

Therefore, the correct answer from the given options is:

[tex]\[ x = \frac{5 \pm 3i}{2} \][/tex]