The Discriminant
Example 1
Use the discriminant to determine the nature of the solutions of this
quadratic equation: 5x2 - 3x + 8 = 0
Solution
The equation has the form ax2 + bx + c = 0 where a = 5, b= -3, and
c = 8.
The equation has the form ax2 + bx
+ c = 0 where a = 5, b = -3, and
c = 8. |
Substitute the values of a, b, and c into the discriminant and simplify. |
b2 - 4ac |
= (-3)2 - 4(5)(8)
= 9 - 160
= -151 |
The discriminant is -151, a negative number.
So the equation 5x2 - 3x + 8 = 0 has no real number solutions.
Example 2
Use the discriminant to determine the nature of the solutions of this
quadratic equation: 9x2 - 6x = -1
Solution
To put the equation in standard form,
add 1 to both sides of the equation.
Now the equation has the form ax2 + bx + c = 0 where a = 9, b
= - 6, and c = 1. |
9x2 - 6x = -1
9x2 - 6x + 1 = 0 |
Substitute the values of a, b, and c into
the discriminant and simplify. |
b2 - 4ac |
= (-6)2 - 4(9)(1) = 36 - 36
= 0 |
The discriminant is 0.
So the equation 9x2 - 6x = -1 has two identical real number solutions. |