### Home > PC3 > Chapter 4 > Lesson 4.1.1 > Problem4-8

4-8.

Recall that not all equations have real solutions. Sometimes the solutions to equations are complex numbers. Use the Quadratic Formula to solve the following equation. Hint: $i^2=-1$

$−13=x^2-4x$

$x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}$

$\sqrt{-9}=3i$

Add $13$ to both sides of the equation so that the quadratic expression is equal to $0$ and the Quadratic Formula can be used.