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Given the equation below, which of the following shows the quadratic formula correctly applied?

[tex]\[ 2x^2 - 9x + 4 = 0 \][/tex]

A. [tex]\[ x = \frac{-9 \pm \sqrt{(-9)^2 - 4(2)(4)}}{2(2)} \][/tex]

B. [tex]\[ x = \frac{-(-9) \pm \sqrt{(-9) - 4(2)(4)}}{2(2)} \][/tex]

C. [tex]\[ x = -(-9) \pm \sqrt{(-9)^2 - 4(2)(4)} \][/tex]

D. [tex]\[ x = \frac{-(-9) \pm \sqrt{(-9)^2 - 4(2)(4)}}{2(2)} \][/tex]


Sagot :

To determine which option correctly applies the quadratic formula to the given equation [tex]\(2x^2 - 9x + 4 = 0\)[/tex], let's first recall the quadratic formula:

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

For our specific equation, [tex]\(a = 2\)[/tex], [tex]\(b = -9\)[/tex], and [tex]\(c = 4\)[/tex].

Let's substitute these values into the quadratic formula:

[tex]\[ x = \frac{-(-9) \pm \sqrt{(-9)^2 - 4 \cdot 2 \cdot 4}}{2 \cdot 2} \][/tex]

Now let's compare this with the given options:

A. [tex]\(x = \frac{-9 \pm \sqrt{(-9)^2 - 4(2)(4)}}{2(2)}\)[/tex]

This option incorrectly uses [tex]\(-9\)[/tex] instead of [tex]\(-(-9)\)[/tex] which should be [tex]\(9\)[/tex]. Incorrect.

B. [tex]\(x = \frac{-(-9) = \sqrt{(-9) - 4(2)(4)}}{2(2)}\)[/tex]

This option incorrectly presents the formula, having an equals sign instead of a plus-minus symbol and an incorrect formula under the square root. Incorrect.

C. [tex]\(x = -(-9) \pm \sqrt{(-9)^2 - 4(2)(4)}\)[/tex]

This option does not divide by [tex]\(2a\)[/tex]. Incorrect.

D. [tex]\(x = \frac{-(-9) \pm \sqrt{(-9)^2 - 4(2)(4)}}{2(2)}\)[/tex]

This option correctly substitutes the values into the quadratic formula.

Thus, option D is the correct application of the quadratic formula to the given equation.