Apolynomial has two terms. check all of the factoring methods that should be considered.

a. common factor
b. difference of cubes
c. sum of cubes
d. difference of squares
e. perfect-square trinomial
f. factoring by grouping

Set $r$ is a set of rectangles such that (1) only the grid points shown here are used as vertices, (2) all sides are vertical or horizontal and (3) no two rectangles in the set are congruent. if $r$ contains the maximum possible number of rectangles given these conditions, what fraction of the rectangles in set $r$ are squares? express your answer as a common fraction.