в арифметической прогрессии найдите а2 и d если а12=-2,а3=7
а3=а1+2d
a12=a1+11d
a1=a3-2d=7-2d
a1=a12-11d=-2-11d
7-2d=-2-11d
-2d+11d=2-7
9d=-5
d=-5/9
a1=7+10/9=73/9
a2=a1+d=73/9-5/9=68/9
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а3=а1+2d
a12=a1+11d
a1=a3-2d=7-2d
a1=a12-11d=-2-11d
7-2d=-2-11d
-2d+11d=2-7
9d=-5
d=-5/9
a1=7+10/9=73/9
a2=a1+d=73/9-5/9=68/9