题目

等差数列{}的公差d＜0,且a2·a4=12,a2+a4=8,则数列{an}的通项公式是 A.an=2n-2(n∈N*)                          B.an=2n+4(n∈N*)C.an=-2n+12(n∈N*)                      D.an=-2n+10(n∈N*) 答案：D解析：a2,a4为x2-8x+12=0的两根，得x1=2,x2=6, ∵公差d＜0, ∴a2=6,a4=2,d=-2.∴an=a2+(n-2)d=6-2(n-2)=10-2n. ∴选D.结合《送往小木屋的信》，我理解“家书抵万金”的含义是：_____________________________________________________ ______________________________________________________ _____