1. 6x*a/3x^2 2. 1-2c/c^3-1 - c-1/c^2+c+1 3. 4a/5b÷2a^2/15b^2 4. 3/x^2-2x*2x-4/x

1. 6xa/3x^2 = 2a/x;2. (1 - 2c)/(c^3 - 1) - (c - 1)/(c^2 + c + 1) =(1 - 2c)/((c - 1)(c^2 + c + 1)) - (c - 1)/(c^2 + c + 1) = (1 - 2c - (c - 1)^2)/((c - 1)(c^2 + c + 1)) = (1 - 2c - c^2 + 2c - 1)/((c - 1)(c^2 + c + 1)) = -c^2/(c^3 - 1); 3. 4a/5b ÷ 2a^2/15b^2 = 4a/5b * 15b^2/2a^2 = 3b/a;4. 3/(x^2 - 2x) * (2x - 4)/x = 3/(x(x - 2)) * (2(x - 2))/x = 6/x^2.