Question

3.等差数列的前项和为若

(A)12                           (B)10                           (C)8               (D)6

Answer 1

C

解析:∵在等差数列{a_n}中,a₂=1,a₃=3,

∴d=a₃－a₂=2,

a₁=a₂－d=1－2=－1,

S₄=4a₁+d=－4+12=8.