r4 + 4·r2 + 4 = (r2 + 2)2
25·z4 - 81·y2 = (5·z2 + 9·y)·(5·z2 - 9·y)
7·a2 - 63·b2 = 7·(a2 - 9·b2) = 7·(a + 3·b)·(a - 3·b)
128·p4 - 72·q2 = 8·(16·p4 - 9·q2) = 8·(4·p2 + 3·q)·(4·p2 - 3·q)
48·q3 - 147·q·s2 = 3·q·(16·q2 - 49·s2) = 3·q·(4·q + 7·s)·(4·q - 7·s)