1.a1+a3=2a2=8 a2=4a2+a4=2a3=12 a3=6d=a3-a2=6-4=2a1=a2-d=4-2=2an=a1+(n-1)d=2+2(n-1)=2n数列{an}的通项公式为an=2n2.Sn=(a1+an)n/2=(2+2n)n/2=n(n+1)a1、ak、S(k+2)成等比数列,则ak²=a1·S(k+2)(2k)²=2...