Unit Test Review

A quadratic equation of the form [tex]0 = ax^2 + bx + c[/tex] has one real number solution. Which could be the equation?

A. [tex]0 = 2x^2 - 4x + 1[/tex]
B. [tex]0 = 2x^2 - 5x + 3[/tex]
C. [tex]0 = -2x^2 - 4x - 2[/tex]
D. [tex]0 = -2x^2 - 3x - 1[/tex]



Answer :

To determine which quadratic equation has exactly one real number solution, we need to examine each equation to find its discriminant.

The discriminant [tex]\(\Delta\)[/tex] of a quadratic equation [tex]\(ax^2 + bx + c = 0\)[/tex] is calculated using the formula:
[tex]\[ \Delta = b^2 - 4ac \][/tex]

A quadratic equation will have:
- Two distinct real number solutions if [tex]\(\Delta > 0\)[/tex]
- Exactly one real number solution if [tex]\(\Delta = 0\)[/tex]
- No real number solutions if [tex]\(\Delta < 0\)[/tex]

Let's calculate the discriminant for each equation:

1. For the equation [tex]\(0 = 2x^2 - 4x + 1\)[/tex]:
[tex]\[ a = 2, \quad b = -4, \quad c = 1 \][/tex]
[tex]\[ \Delta = (-4)^2 - 4 \cdot 2 \cdot 1 = 16 - 8 = 8 \][/tex]
Since [tex]\(\Delta = 8\)[/tex], which is greater than 0, this equation has two distinct real number solutions.

2. For the equation [tex]\(0 = 2x^2 - 5x + 3\)[/tex]:
[tex]\[ a = 2, \quad b = -5, \quad c = 3 \][/tex]
[tex]\[ \Delta = (-5)^2 - 4 \cdot 2 \cdot 3 = 25 - 24 = 1 \][/tex]
Since [tex]\(\Delta = 1\)[/tex], which is greater than 0, this equation has two distinct real number solutions.

3. For the equation [tex]\(0 = -2x^2 - 4x - 2\)[/tex]:
[tex]\[ a = -2, \quad b = -4, \quad c = -2 \][/tex]
[tex]\[ \Delta = (-4)^2 - 4 \cdot (-2) \cdot (-2) = 16 - 16 = 0 \][/tex]
Since [tex]\(\Delta = 0\)[/tex], this equation has exactly one real number solution.

4. For the equation [tex]\(0 = -2x^2 - 3x - 1\)[/tex]:
[tex]\[ a = -2, \quad b = -3, \quad c = -1 \][/tex]
[tex]\[ \Delta = (-3)^2 - 4 \cdot (-2) \cdot (-1) = 9 - 8 = 1 \][/tex]
Since [tex]\(\Delta = 1\)[/tex], which is greater than 0, this equation has two distinct real number solutions.

Among the given equations, the one that has exactly one real number solution is:
\[
0 = -2x^2 - 4x - 2