1) (с-2)(с+3)-(с-1)^2 = с^2-2с+3с-6-(с^2-2c+1) = с^2-2с+3с-6-с^2+2c-1 = 3c-7
2) 3(a+c)^2-6ac = 3(а^2+2ас+с^2) -6ас = 3а^2+6ас+3с^2-6ас = 3а^2+3с^2 = 3(а^2+с^2)
3) (p-3)(p^2+3p+9)-p^3 = р^3-3р^2+3р^2-9р+9р-27-р^3 = -27
