This task is useful for helping pupils begin to see the underlying relationship between the coefficients of a quadratic, and the factorised version of the expression.  Particular attention should be drawn to the cases where the coefficient of x is 0.  This leads to a subsequent discussion of the special case of a difference of two squares.  Many teachers teach it as a separate and entirely disconnected from the general case of a quadratic, when in fact it is a natural progression. 

Credit:  @chrismcgrane84