Cho A = 1/1.2 + 1/3.4 + 1/5.6 +...+ 1/49 + 1/50
B = 1/1 + 1/2 + 1/3 + 1/4 +...+ 1/49 + 1/50
C = 1/2 + 1/4b+ 1/6 +...+ 1/48 + 1/50 Chung Minh A=B-2C
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