1.(C-2)(c+3)-(c-1)^2+3(5+c)^2-6c = c^2+3c-2c-6-(c^2-2c+1)+3(25+10c+c^2)-6c = c^2+3c-2c-6-c^2+2c-1+75+30c+3c^2-6c = 27c+68+3c^2
2.
1)a+2b/a^2-4b^2 = a+2b/(a-2b)(a+2b) = 1/a-2b
2)a^3-8/(a^2+2a+4) = (a-2)(a^2+2a+4)/a^2+2a+4 = a-2
3)x^3+1/x^2-x+1 = (x+1)(x^2-x+1)/x^2-x+1 = x+1