Question

\(\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+.....+\frac{1}{73.76}\)

Answer 1

A=\(\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+...+\frac{1}{73.76}\)

3A=3(\(\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+...+\frac{1}{73.76}\))

3A=\(\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{73.76}\)

3A=\(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{73}+\frac{1}{76}\)

3A=\(\frac{1}{4}-\frac{1}{76}\)

3A=\(\frac{9}{38}\)

A=\(\frac{9}{38}\):3

A=\(\frac{3}{38}\)

Answer 2

đặt A=1/4.7+1/7.10+...+1/73.76

3A=1/4-1/7+1/7-1/10+...+1/ 73 -1/ 76
 

Answer 3

\(A=\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+...+\frac{1}{73.76}\)

\(3A=\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{73.76}\)

\(3A=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{73}-\frac{1}{76}\)

\(3A=\frac{1}{4}-\frac{1}{76}\)

\(3A=\frac{9}{38}\)

\(A=\frac{3}{38}\)

Answer 4

Đặt biểu thức là A. Ta có:

A = \(\frac{1}{4.7}\)+  \(\frac{1}{7.10}\)+.....+ \(\frac{1}{73.76}\)

3A = 3.(\(\frac{1}{4.7}\)+ \(\frac{1}{7.10}\)+ ....+ \(\frac{1}{73.76}\))

      = \(\frac{3}{4.7}\)+ \(\frac{3}{7.10}\)+.....+ \(\frac{3}{73.76}\)

      =\(\frac{1}{4}\)- \(\frac{1}{7}\)- \(\frac{1}{7}\)- \(\frac{1}{10}\)+.....+ \(\frac{1}{73}\)- \(\frac{1}{76}\)

      =\(\frac{1}{4}\)- \(\frac{1}{76}\)=\(\frac{9}{38}\)

   => A=\(\frac{9}{38}\): 3 = \(\frac{3}{38}\)

bài đơn giản. Mik bớt số hạng thứ 3 đi cko tính nhanh. Bn thêm số hạng thứ 3 vào (\(\frac{1}{10.13}\) ) hay để như mik làm đều đúng. Nhớ k cko mik nhé. Thanks