(аn) a1+a3=24 a2*a3=60 d-? a1-? арифметическая прогрессия . 50

A1+a1+4d=24⇒a1+2d=12⇒a1=12-2d
(a1+d)(a1+2d)=60
(12-2d+d)(12-2d+2d)=60
12(12-d)=60
12-d=60/12=5
d=12-5=7
a1=12-2*7=12-14=-2

1)a₁+a₃=24
a₁+a₁+2d=24
2a₁+2d=24
a₁+d=12
a₁=12-d
2)a₂*a₃=60
(12-d+d)(12-d+2d)=60
12(12+d)=60
12+d=5
d=5-12=-7
a₁=12-(-7)=19
ответ:d=-7;a₁=19