Question

1 . TÌM X , BIẾT

A ) X +\(\frac{4}{5}=\frac{7}{10}\)

B ) \(\frac{2}{3}x-\frac{3}{4}=2\frac{5}{6}\)

 

2 TÍNH TỔNG

\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}\)

 

 

Answer 1

1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7+1/7.8+1/8.9

=1-1/2+1/2-1/3+1/3-1/4+...+1/8-1/9

=1-1/9

=8/9

Answer 2

A) \(x = {7 \over 10}- {8 \over10} \)

\(x = {-1 \over 10}\)

B)\({2 \over3}x = 2{5 \over 6}-{3 \over4}\)

\({2 \over3}x = {25 \over 12}\)

\(x = {25 \over 12}/{2 \over3} \)

\(x = {25\over 8}\)

2/ Tính tổng:

\( = {8 \over 9}\)