Question

What value is added to both sides of the equation x2 − 6x = 10 in order to solve by completing the square?

Answer 1

$x^2-6x=10\\\\x^2-2\cdot x\cdot3=10\ \ \ |+3^2=9\\\\\underbrace{x^2-2\cdot x\cdot3+3^2}_{(a-b)^2=a^2-2ab+b^2}=19\\\\(x-3)^2=19$

Answer: 9