Mình nhầm

tk:Đặt A = 1/3×5 + 1/5×7 + 1/7×9 + ... + 1/97×99 + 1/99 x 101

2A = 2/3×5 + 2/5×7 + 2/7×9 + ... + 2/97×99 + 2/99 x 101

2A = 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + ... + 1/97 - 1/99 + 1/99 - 1/101

2A = 1/3 - 1/101

2A = 98/303

A =98/303 : 2

A = 49/303 

tk:Đặt A = 1/3×5 + 1/5×7 + 1/7×9 + ... + 1/97×99 + 1/99 x 101

2A = 2/3×5 + 2/5×7 + 2/7×9 + ... + 2/97×99 + 2/99 x 101

2A = 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + ... + 1/97 - 1/99 + 1/99 - 1/101

2A = 1/3 - 1/101

2A = 26/101

A = 26/101 : 2

A = 13/101

98,72