Question

[Hiếu Hoàng Thị]

Giúp mik mha

Answer 1

[.]

\(B=\frac{1}{1.4}+\frac{2}{4.10}+\frac{3}{10.19}+\frac{4}{19.31}\)

\(3B=\frac{3}{1.4}+\frac{6}{4.10}+\frac{9}{10.19}+\frac{12}{19.31}\)

\(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{10}+\frac{1}{10}-\frac{1}{19}+\frac{1}{19}-\frac{1}{31}\)

\(=1-\frac{1}{31}=\frac{31}{31}-\frac{1}{31}=\frac{30}{31}\)

\(\Rightarrow B=\frac{30}{31}\div3=\frac{10}{31}\)

Vậy \(B=\frac{10}{31}\).

Answer 2

[🅼🅸🆄 ▬▬ι═══════ﺤ 🅺8]

       B = 1/1.4 + 2/4.10 + 3/10.19 + 4/19.31

=> 3B = 3/1.4 + 6/4.10 + 9/10.19 + 12/19.31

=> 3B = 1 - 1/4 + 1/4 - 1/10 + 1/10 - 1/19 + 1/19 - 1/31

=> 3B = 1 - 1/31 

=> 3B = 30/31

=> B  = 30/31 : 3

=> B = 10/31

Vậy B = 10/31