4
49x^8 - 3.24x^6 = x^6(49x^2-1.8^2) = x^6(7x-1.8)(7x+1.8)
5
0.01x^2 + 0.14xy + 0.49y^2 = (0.1x + 0.7y)^2
6
(a-3)(a+2) - (a-1)^3 = a^2+2a-3a-6 - (a^3-3a^2+3a-1)
= a^2-a-6-a^3+3a^2-3a+1 = -a^3 + 4a^2 - 4a -5
7
2n^2 - 3an - 10n + 15a = 5(3a-2n)-n(3a-2n) = (5-n)(3a-2n)