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lethimyhanh.c3thuthua
2 năm trước
1)Xét các số ak có dạng: ak = 3k^2 + 3k với k ∈ N* . a. Chứng minh: ak = (k + 1)^3 − k ^3 − 1. b. Tính S = a1 + a2 + a3 + ... + a98 + a99 2)Cho hình thang ABCD ( AB// CD) . Trên cạnh AD lấy các điểm M N, sao cho AM =MN= ND , trên cạnh BC lấy các điểm P Q, sao cho BP =PQ =QC . Giả sử rằng AB// MP// NQ// CD . Chứng minh 3MP= 2AB+ CD
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