a6+a8=15
a2*a12=56
a1+5d+a1+7d=15
2a1+12d=15|:2
a1+6d=7.5
a1=7.5-6d
(a1+d)(a1+11d)=56
(7.5-6d+d)(7.5-6d+11d)=56
(7.5-5d)(7.5+5d)=56
7.5^2-(5d)^2=56
56.25-25d^2=56
25d^2=0.25
d^2=0.01
d=0.1
ответ: 0,1
a6+a8=15
a2*a12=56
a1+5d+a1+7d=15
2a1+12d=15|:2
a1+6d=7.5
a1=7.5-6d
a2*a12=56
(a1+d)(a1+11d)=56
(7.5-6d+d)(7.5-6d+11d)=56
(7.5-5d)(7.5+5d)=56
7.5^2-(5d)^2=56
56.25-25d^2=56
25d^2=0.25
d^2=0.01
d=0.1
ответ: 0,1