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trantungthien


tim x biet
a) 1/5.8+1/8.11+............+1/x.(x+1)=101/1540
B)1+1/3+1/6+........+1/x.(x+1):2=1993+1991/1993
khó lam an tu tu thoi keo nghen nhe anh em hoc nua hoc mai














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a) 1/5.8+1/8.11+............+1/x.(x+1)=101/1540
B)1+1/3+1/6+........+1/x.(x+1):2=1993+1991/1993
khó lam an tu tu thoi keo nghen nhe anh em hoc nua hoc mai