câu 2Sn/Sm = n2/m2 =>n(U1+Un) / m(U1+Um) =n^2/m2=> (U1+Un)/(U1+Um) =n/m => m(2U1+nd-d)=n(2U1+md-d) => (m-n)(2U1-d) =0=>2U1=dMặt khác : U2014/U2009 =( U1 +2013d)/(U1+2008d)=4027/4017câu 1
câu 2Sn/Sm = n2/m2 =>n(U1+Un) / m(U1+Um) =n^2/m2=> (U1+Un)/(U1+Um) =n/m => m(2U1+nd-d)=n(2U1+md-d) => (m-n)(2U1-d) =0=>2U1=dMặt khác : U2014/U2009 =( U1 +2013d)/(U1+2008d)=4027/4017