Question

A = 1/20+1/30+1/42+1/56+1/72

Answer 1

=5/36

đúng thì k mình nhé 

làm ơn giúp mình mình đang bị âm

Answer 2

A = 1/20 +   1/30 + 1/42   +   1/56  + 1/72

A= 1/4x5 + 1/5x6 + 1/6x7 + 1/7x8 + 1/8x9

A= 1/4 - 1/5 + ......................+ 1/8 - 1/9

A= 1/4 - 1/9

A=     5/36

Answer 3

\(A=\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}\)

\(A=\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{7.8}+\frac{1}{8.9}\)

\(A=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{8}-\frac{1}{9}\)

\(A=\frac{1}{4}-\frac{1}{9}\)

\(\Rightarrow A=\frac{5}{36}\)