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已知在平面直角坐标系中,有三点A(1,0)、B(﹣1,2)、C(﹣2,2),请用有向线段表示A到B,B到C,C到A的位移.
等差数列{an}的前n项和为Sn,a3=3,S4=10,则 ∑k=1n1Sk =____.