r^4 + 4·r^2 + 4 = (r^2 + 2)^2
25·z^4 - 81·y^2 = (5·z^2 + 9·y)·(5·z^2 - 9·y)
7·a^2 - 63·b^2 = 7·(a^2 - 9·b^2) = 7·(a + 3·b)·(a - 3·b)
128·p^4 - 72·q^2 = 8·(16·p^4 - 9·q^2) = 8·(4·p^2 + 3·q)·(4·p^2 - 3·q)
48·q^3 - 147·q·s^2 = 3·q·(16·q^2 - 49·s^2) = 3·q·(4·q + 7·s)·(4·q - 7·s)