由a2+a12=2a7得a2+a7+a12=12,即3a7=12,a7=4,分别代入a2+a7+a12=12和a2*a7*a12=28得a2+a12=8,a2*a12=7,联立成方程组并解之得a2=1,a12=7或者a2=7,a12=1,设首项为a1,公差为d,分别联解a1+d=1,a1+6d=7和a1+d=7,a1+6d=1得a...