Ответ: 10, 7, 4.

Объяснение:

[tex]\displaystyle\\a_1,\ \ a_2=a_1+d,\ \ a_3=a_1+2d\\\\\left \{ {{a_1+a_1+d+a_1+2d=21} \atop {a_1*a_2=70}} \right. \ \ \ \ \left \{ {{3*a_1+3*d=21\ |:3} \atop {a_1*a_2=70}} \right. \ \ \ \ \left \{ {{a_1+d=a_2=7} \atop {a_1*a_2=70}} \right. \\\\\\\left \{ {{a_2=7} \atop {a_1*7=70\ |:7}} \right. \ \ \ \ \ \ \left \{ {{a_1+d=7} \atop {a_1=10}} \right. \ \ \ \ \left \{ {{10+d=7} \atop {a_1=10}} \right. \ \ \ \ \ \left \{ {{d=-3} \atop {a_1=10}} \right. .\ \ \ \ \ \ \Rightarrow\\\\[/tex]

[tex]a_1=10\\\\a_2=10+(-3)=7\\\\a_3=7+(-3)=4.[/tex]