Quadratic Equations with Imaginary Solutions
We can get imaginary solutions by completing the square.
Example 1
An equation with imaginary solutions
Find the complex solutions to x2 - 4x + 12 = 0.
Solution
Because the quadratic polynomial cannot be factored, we solve the equation by
completing the square.
x2 - 4x + 12 |
= 0 |
The original equation |
x2 - 4x |
= -12 |
Subtract 12 from each side. |
x2 - 4x + 4 |
= -12 + 4 |
One-half of -4 is -2, and (-2)2 = 4. |
(x - 2)2 |
= -8 |
|
x - 2 |
= ± |
Even-root property |
x |
= 2 ± i |
|
x |
=
|
|
Check these values in the original equation. The solution set is {}.
|