已知等差数列an的公差d不等于0

1.S5=5a1+10d=5(a1+2d)=70a1+2d=14a3=14a7^2=a2×a22(a3+4d)^2=(a3-d)(a3+19d)a3=14代入,整理,得d(d-4)=0d=0(已知d不等于0,舍去)或d=4a1=a3-2d=14-8=6an=a1+(n-1)d=6+4(n-1)=4n+2数列{an}的通项公式为an=4n+22.S...