Объяснение:

[tex]\left \{ {{a_1+a_6=-12,6} \atop {a_5-a_2=-9}} \right.\ \ \ \ \ \left \{ {{a_1+a_1+5d=-12,6} \atop {a_1+4d-a_1-d=-9}} \right. \ \ \ \ \left \{ {{2a_1+5d=-12,6} \atop {3d=-9\ |:3}} \right.\ \ \ \ \left \{ {{2a_1+5*(-3)=-12,6} \atop {d=-3}} \right.[/tex]

[tex]\left \{ {{2a_1-15=-12,6} \atop {d=-3}} \right. \ \ \ \ \left \{ {{2a_1=2,4\ |:2} \atop {d=-3}} \right. \ \ \ \ \ \left \{ {{a_1=1,2} \atop {d=-3}} \right. .[/tex]

Ответ: a₁=1,2    d=-3.