`~rai~`
\(\text{Ta có:}\\+)a+b=2\\\Rightarrow (a+b)^2=2^2\\\Leftrightarrow a^2+2ab+b^2=4\\\Leftrightarrow 6+2ab=4\quad\text{(do }a^2+b^2=6)\\\Leftrightarrow 2ab=-2\\\Leftrightarrow ab=-1.\\+)a^3+b^3\\=a^3+b^3+3a^2b+3ab^2-3a^2b-3ab^2\\=(a^3+3a^2b+3ab^2+b^3)-(3a^2b+3ab^2)\\=(a+b)^3-3ab(a+b)\\=2^3-3.(-1).2\\=14.\\\to\text{Chọn ý C.}\)