Ta có 2/40 + 2/88 + 2/154 + ... + 2/x( x + 3) = 202
=> 2/5 x 8 + 2/8 x 11 + ... + 2/x( x + 3 ) = 202
=> 1/5 x 8 + 1/8 x 11 + ... + 1/x( x + 3 ) = 202 : 2
=> 1/5 - 1/8 + 1/8 - 1/11 + ... + 1/x - 1/x + 3 = 101
=> 1/5 - 1/x + 3 = 101
=> 1/x + 3 = 1/5 - 101
=> 1/X + 3 = 504/5
=> 504(x + 3 ) = 5
\(\frac{2}{40}+\frac{2}{888}+\frac{2}{154}+......+\frac{2}{x.\left(x+3\right)}=202\)
\(=\frac{2}{5.8}+\frac{2}{888}+\frac{2}{11.14}+............+\frac{2}{x.\left(x+3\right)}=202\)
=>Đề sai bạn sửa lại nha
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