已知等差數(shù)列{a_n}的前n項(xiàng)和為S_n,若a₄+a₅=18,則S₈等于(    )

A.18                  B.36                  C.54             D.72

已知等差數(shù)列{a_n}的前n項(xiàng)和為S_n,若=a₁+a₂₀₀,且A、B、C三點(diǎn)共線(該直線不過點(diǎn)O),則S₂₀₀等于(    )

A.100              B.101                  C.200              D.201

已知等差數(shù)列{a_n}的前n項(xiàng)和為S_n,若a₄=18-a₅,則S₈ 等于（    ）

A.18            B.36               C.54                 D.72

已知等差數(shù)列{a_n}的前n項(xiàng)和為S_n,若S₉=18,S_n=240,a_n-4=30,則n等于

A.18                     B.17                  C.16                  D.15

已知等差數(shù)列{a_n}的前n項(xiàng)和為S_n,若=a₁+a₂₀₀,且A、B、C三點(diǎn)共線(該直線不過點(diǎn)O),則S₂₀₀等于(    )

A.100              B.101              C.200             D.201