Rút gọn Q=(x^2+3x)/(x^3+3x^2+9x+27)+3/(x^2+9):(1/(x-3)-6x/(x^3-3x^2+9x-27)21/26Cho Q=x2+3xx3+3x2+9x+27+3x2+9:1x-3-6xx3-3x3+9x-27 Rút gọn Q ta được: Q=1x2+9 Q=x-3x+3 Q=1x-3 Q=x+3x-3Giải thíchĐK: x≠±3Q=x2+3x+3x+9(x2+9)(x+3):x2+9-6x(x-3)(x2+9)=x+3x-3 Đáp án D