Missing constant: 100
perfect square (a - b)^2 = a^2 - 2ab + b^2
In this case
20x = 2 * x * 10
10^2 = 100
(x - 10)^2 = x^2 - 20x + 100
relating to or denoting a system of numbers and arithmetic based on the number ten, tenth parts, and powers of ten.
it alot will look like this 4.4