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Which values of [tex]x[/tex] are solutions to this equation?

[tex]-\frac{1}{2} x^2 + 5x = 8[/tex]

A. [tex]-8[/tex]

B. [tex]8[/tex]

C. [tex]-2[/tex]

D. [tex]-1.5[/tex]

E. [tex]2[/tex]

F. [tex]11.5[/tex]


Sagot :

To solve the quadratic equation
[tex]\[ -\frac{1}{2} x^2 + 5x = 8, \][/tex]
let's first rewrite it in standard form, which is
[tex]\[ ax^2 + bx + c = 0. \][/tex]

Subtract 8 from both sides of the equation:
[tex]\[ -\frac{1}{2} x^2 + 5x - 8 = 0. \][/tex]

Here, we can identify the coefficients:
[tex]\[ a = -\frac{1}{2}, \quad b = 5, \quad c = -8. \][/tex]

Next, we will use the quadratic formula to find the solutions for \( x \):
[tex]\[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}. \][/tex]

1. Calculate the discriminant (\( \Delta \)):
[tex]\[ \Delta = b^2 - 4ac. \][/tex]
Plugging in the values, we get:
[tex]\[ \Delta = 5^2 - 4 \left(-\frac{1}{2}\right)(-8). \][/tex]
Simplify the expression:
[tex]\[ \Delta = 25 - 4 \left(-\frac{1}{2}\right)(-8) = 25 - 16 = 9. \][/tex]

2. Determine the square root of the discriminant:
[tex]\[ \sqrt{\Delta} = \sqrt{9} = 3. \][/tex]

3. Apply the quadratic formula for the two possible values of \( x \):
[tex]\[ x = \frac{-b \pm \sqrt{\Delta}}{2a}. \][/tex]

So we have:
[tex]\[ x = \frac{-5 \pm 3}{2 \left(-\frac{1}{2}\right)}. \][/tex]

4. Calculate the two solutions separately:
[tex]\[ x_1 = \frac{-5 + 3}{-1} = \frac{-2}{-1} = 2, \][/tex]
[tex]\[ x_2 = \frac{-5 - 3}{-1} = \frac{-8}{-1} = 8. \][/tex]

Therefore, the values of \(x\) that satisfy the equation
[tex]\[ -\frac{1}{2} x^2 + 5x = 8 \][/tex]
are
[tex]\[ x = 2 \][/tex]
and
[tex]\[ x = 8. \][/tex]

So among the given options, the solutions are:
- \(2\)
- \(8\)

The other options (-8, -2, -1.5, 11.5) do not satisfy the equation.
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