In effect, each row (and each column) is a permutation of four distinct numbers (or symbols). Such arrays have proved useful for a variety of purposes. Suppose, for example, you wanted to check the ...

Rewrite \(y = {x^2} - 6x + 11\) in the form \(y = {(x - b)^2} + c\). To get \(b\) (the number inside the bracket), halve the coefficient (number in front) of the second term in the original equation.