### Home > AC > Chapter 10 > Lesson 10.4.2 > Problem10-139

10-139.

Solve the quadratic equation below twice, once using the Quadratic Formula and once by completing the square. Which was easier?

$x^2-10x+21=-4$

Quadratic Formula: $x = \frac { - b \pm \sqrt { b ^ { 2 } - 4 a c } } { 2 a }$

Complete the Square: Subtract 21 on both sides. Then add a constant to both sides to get: $(x-5)^2$ on the left side.