Question

3/1.4+3/4.7+3/7.10+3/10.13

Answer 1

3/1.4+3/4.7+3/7.10+3/10.13

=1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 + 1/10 - 1/13

=1 - 1/13

=12/13

Answer 2

#)Trả lời :

Gọi tổng trên là A 

\(A=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}\)

\(A=3-\frac{3}{4}+\frac{3}{4}-\frac{3}{7}+\frac{3}{7}-\frac{3}{10}+\frac{3}{10}-\frac{3}{13}\)

\(A=3-\frac{3}{13}\)

\(A=2\frac{10}{13}=\frac{36}{13}\)

               #~Will~be~Pens~#

Answer 3

\(\frac{3}{1\cdot4}+\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+\frac{3}{10\cdot13}\)

\(=3-\frac{3}{4}+\frac{3}{4}-\frac{3}{7}+\frac{3}{7}-\frac{3}{10}+\frac{3}{10}-\frac{3}{13}\)

\(=3-\frac{3}{13}\)

\(=\frac{36}{13}\)

Answer 4

Hoàng Nguyên Hiếu làm sai rồi kìa

Answer 5

\(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}\)

\(=3-\frac{3}{4}+\frac{3}{4}-\frac{3}{7}+\frac{3}{7}-\frac{3}{10}+\frac{3}{10}-\frac{3}{13}\)

\(=3-\frac{3}{13}\)

\(=\frac{36}{13}\)

Answer 6

1 với 4;4 với 7;.........đều hơn kém nhau 3 đơn vị mà công thức là\(\frac{1}{x.\left(x+1\right)}=\frac{1}{x}-\frac{1}{x+1}\)

Answer 7

GỌI \(\frac{3}{1\cdot4}+\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+\frac{3}{10\cdot13}=A\)

\(\Rightarrow A=3\left(\frac{1}{1\cdot4}+\frac{1}{4\cdot7}+\frac{1}{7\cdot10}+\frac{1}{10\cdot13}\right)\)

\(\Rightarrow A=3\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}\right)\)

\(\Rightarrow A=3\left(1-\frac{1}{13}\right)=3\cdot\frac{12}{13}=\frac{36}{13}\)

CÁCH NÀY VỪA DỄ LÀM VỪA DỄ HIỂU , 

HK TỐT ~

Answer 8

\(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}\)

\(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}\)

\(=1-\frac{1}{13}=\frac{13-1}{13}=\frac{12}{13}\)