⇒1=(Ax+B)(x2−x+1)+(Cx+D)(x2+x+1) ⇒1=(Ax3+Ax2+Ax+Bx2−Bx+B)+(Cx3+Cx2+Cx+Dx2+Dx+D) ⇒ 1=(A+C)x3+(−A+B+C+D)x2+(A−B+C+D)x+(B+D) On comparing, the coefficient of like powers on both sides, we get A+C=0 ...…(i) −A+B+C+D=0 ......(ii) A−B+C+D=0 .......(iii) and B+D=1 ......(iv) On adding Eqs. (ii) and (iii), we get 2(C+D)=0 ⇒ C+D=0