1) = (c⁴-2c²)+(c³-2c) = c²(c²-2)+c(c²-2) = c(c²-2)(c+1)
2) = (-y⁶-y⁵)+(y⁴+y³) = -y⁵(y+1)+y³(y+1) = y³(y+1)(1-y²)
3) = (16ab²+32ac²)+(-10c³-5b²c) = 16a(b²+2c²)-5c(b²+2c²) = (b²+c²)(16a-5c)
4) = (6a³+2ab²)+(-21a²b-7b³) = 2a(3a²+b²)-7(3a²+b²) = (3a²+b²)(2a-7)