how many distinct pairs of disjoint non-empty subsets of a are there, the union of which is all of a?

Can you me find the missing length. i attached an image.

Which shows one way to determine the facts of x3+4x2+5x+20 by grouping

Given: lkm jkm, clmk prove: alkmajkm jmk. choose the word that completes the sentence correctly. proof: lkm jkm and lmk * umk are given. km km by the property of congruence. equivalence symmetric reflexive transitive