Question

[Trần Khởi My]

Tính tổng :

B= 1/1.5+1/5.9+1/9.13+...+1/93.97

C= 3/1.3+3/3.5+3/5.7+...+3/97.99

D= 1/10+1/15+1/20+...+1/120

E= 2/15+2/35+2/63+...+2/399

Ai nhanh mk tick làm nhanh nhé mk cần gấp lắm 

Answer 1

[@Hacker.vn]

• \(B=\frac{1}{1.5}+\frac{1}{5.9}+\frac{1}{9.13}+...+\frac{1}{93.97}\)

           \(4.B=\frac{4}{1.5}+\frac{4}{5.9}+\frac{4}{9.13}+...+\frac{4}{93.97}\) 

            \(4.B=1-\frac{1}{5}+\frac{1}{5}-\frac{1}{9}+\frac{1}{9}-\frac{1}{13}+...+\frac{1}{93}-\frac{1}{97}\)

            \(4.B=1-\frac{1}{97}\)

             \(4.B=\frac{96}{97}\)

                 \(B=\frac{96}{97}:4\)

                 \(B=\frac{24}{97}\)