\left \{ {{a_1+a__1+6d=16} \atop {a_1-a_1-6d=-12}} \right. <=>" alt="\left \{ {{a_1+a_7=16} \atop {a_1-a_7=-12}} \right. <=> \left \{ {{a_1+a__1+6d=16} \atop {a_1-a_1-6d=-12}} \right. <=>" align="absmiddle" class="latex-formula">
\left \{ {{2a_1+6d=16} \atop {-6d=-12}} \right. <=> \left \{ {{a_1+3d=8} \atop {d=2}} \right. <=>" alt="<=> \left \{ {{2a_1+6d=16} \atop {-6d=-12}} \right. <=> \left \{ {{a_1+3d=8} \atop {d=2}} \right. <=>" align="absmiddle" class="latex-formula">
\left \{ {{d=2} \atop {a_1=8-3d=8-3*2=2}} \right. =>S_{10}=\frac{2a_1+9d}{2}*10= \\ =\frac{2*2+9*2}{2}*10=110" alt="<=> \left \{ {{d=2} \atop {a_1=8-3d=8-3*2=2}} \right. =>S_{10}=\frac{2a_1+9d}{2}*10= \\ =\frac{2*2+9*2}{2}*10=110" align="absmiddle" class="latex-formula">