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Select the two values of [tex]$x$[/tex] that are roots of this equation:

[tex]\[ x^2 - 5x + 2 = 0 \][/tex]

A. [tex]$x=\frac{5+\sqrt{17}}{2}$[/tex]

B. [tex]$x=\frac{5-\sqrt{17}}{2}$[/tex]

C. [tex][tex]$x=\frac{5+\sqrt{33}}{2}$[/tex][/tex]

D. [tex]$x=\frac{5-\sqrt{33}}{2}$[/tex]


Sagot :

To find the roots of the quadratic equation [tex]\( x^2 - 5x + 2 = 0 \)[/tex], we can use the quadratic formula, which states:

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

For the given equation [tex]\( x^2 - 5x + 2 = 0 \)[/tex], we identify the coefficients:
- [tex]\( a = 1 \)[/tex]
- [tex]\( b = -5 \)[/tex]
- [tex]\( c = 2 \)[/tex]

Step 1: Compute the discriminant [tex]\(\Delta\)[/tex].
[tex]\[ \Delta = b^2 - 4ac = (-5)^2 - 4 \cdot 1 \cdot 2 = 25 - 8 = 17 \][/tex]

Step 2: Calculate the roots using the quadratic formula.
[tex]\[ x_{1,2} = \frac{-b \pm \sqrt{\Delta}}{2a} \][/tex]

Since [tex]\( b = -5 \)[/tex] and [tex]\( \Delta = 17 \)[/tex]:
[tex]\[ x = \frac{5 \pm \sqrt{17}}{2} \][/tex]

Thus, the roots are:
[tex]\[ x_1 = \frac{5 + \sqrt{17}}{2}, \quad x_2 = \frac{5 - \sqrt{17}}{2} \][/tex]

Step 3: Identify the correct options given in the problem.
The equations corresponding to the given roots and answers are:
- Option A: [tex]\( x = \frac{5 + \sqrt{17}}{2} \)[/tex]
- Option B: [tex]\( x = \frac{5 - \sqrt{17}}{2} \)[/tex]
- Option C: [tex]\( x = \frac{5 + \sqrt{33}}{2} \)[/tex]
- Option D: [tex]\( x = \frac{5 - \sqrt{33}}{2} \)[/tex]

From the calculations:
The correct roots are:
[tex]\[ x_1 = \frac{5 + \sqrt{17}}{2}, \quad x_2 = \frac{5 - \sqrt{17}}{2} \][/tex]
Matching these with the given options, we identify the correct options as:
- Option A: [tex]\( x = \frac{5 + \sqrt{17}}{2} \)[/tex]
- Option B: [tex]\( x = \frac{5 - \sqrt{17}}{2} \)[/tex]

Therefore, the correct selections for the roots are:
[tex]\[ \boxed{A \text{ and } B} \][/tex]