Answer
It's better to memorize the rule for the square of a binomial $(x+a)^2$.
Work Step by Step
The FOIL(First, Outer, Inner, Last) method is based on the distribution of multiplication over addition which is surely the appropriate method for the multiplication of two binomials but still, it is time-consuming due to the increased number of steps. Thus, it is better to memorize the rule for the square of a binomial $(x+a)^2$.
