a5+a6=19x2=38
a5+a6=2a1+9d=2+9d=38
d=4
an=a1+(n-1)d=1+4n-4=4n-3
等差数列{an},a1=1,a5,a6的算术平均数为19,求d及an.
等差数列{an},a1=1,a5,a6的算术平均数为19,求d及an.
数学人气：878 ℃时间：2020-03-30 04:35:51
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