A = 1/1 - 1/2 + 1/2 - ....-1/50 = 1-1/50 = 49/50
B = 1/2 . (1/3 - 1/7 + 1/7 -.....-1/27) = 1/2. (1/3 - 1/27)
B = 1/2. 8/27 = 4/27
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ai lam dc mik tick cho
tính nhanh (1x2)^-1+(2x3)^-1+(3x4)^-1+...+(2014x2015)^-1
Tìm A biết A 1 /1x2+1 /2x3 +1 /3x4 ..... +1 /18x19+ 1 /19x20
Tính: 1+1/1x2+1/2x3+1/3x4+1/4x5+........+1/99x100+1/100x101