Question

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Bài 1b nhá các bạn

Answer 1

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Hok tốt !

Answer 2

Thank

Answer 3

Mình xem có đúng đề mô

Answer 4

Đặt:\(A=1+\frac{1}{2}.\left(1+2\right)+\frac{1}{3}.\left(1+2+3\right)+......+\frac{1}{20}.\left(1+2+3+....+20\right)\)

\(\Rightarrow A=1+\frac{\left(1+2\right).2}{2.2}+\frac{\left(1+3\right).3}{3.2}+.........+\frac{\left(1+20\right).20}{20.2}\)

\(\Rightarrow A=\frac{2}{2}+\frac{3.2}{2.2}+\frac{4.3}{3.2}+.................+\frac{21.20}{20.2}\)

\(\Rightarrow A=\frac{2}{2}+\frac{3}{2}+\frac{4}{2}+.......+\frac{21}{2}\)

\(\Rightarrow A=\frac{1}{2}.\left(2+3+4+...+21\right)=\frac{1}{2}.\frac{\left(2+21\right).20}{2}=\frac{1}{2}.\frac{23.20}{2}=\frac{23.2.2.5}{2.2}=23.5=115\)

Vậy A=115

Chúc bn học tốt

Answer 5

Thank bạn nhiều