Question

A=\(\frac{16}{20.24}+\frac{16}{24.28}+\frac{16}{28.32}+....+\frac{16}{76.80}\)

Answer 1

\(A=4\left(\frac{1}{20}-\frac{1}{80}\right)=4.\frac{3}{80}=60\)

Answer 2

\(A=\frac{16}{20\cdot24}+\frac{16}{24\cdot28}+\frac{16}{28\cdot32}+...+\frac{16}{76\cdot80}\)

\(A=4\left[\frac{4}{20\cdot24}+\frac{4}{24\cdot28}+\frac{4}{28\cdot32}+...+\frac{4}{76\cdot80}\right]\)

\(A=4\left[\frac{1}{20}-\frac{1}{24}+...+\frac{1}{76}-\frac{1}{80}\right]\)

\(A=4\left[\frac{1}{20}-\frac{1}{80}\right]\)

\(A=4\left[\frac{4}{80}-\frac{1}{80}\right]=4\cdot\frac{3}{80}=\frac{4\cdot3}{80}=\frac{1\cdot3}{20}=\frac{3}{20}\)

Answer 3

\(A=\frac{16}{20\cdot24}+\frac{16}{24\cdot28}+...+\frac{16}{76\cdot80}\)

\(A=\frac{4^2}{\left(5\cdot6\right)\cdot4^2}+\frac{4^2}{\left(6\cdot7\right)\cdot4^2}+...+\frac{4^2}{\left(19\cdot20\right)\cdot4^2}\)

\(A=\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+...+\frac{1}{19\cdot20}\)

\(A=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{19}-\frac{1}{20}=\frac{1}{5}-\frac{1}{20}=\frac{3}{20}\)

Answer 4

mk sai

Answer 5

༉Ƙεηηү♕ℌυỳηɦ ͜✿҈

\(A=\frac{16}{20\cdot24}+\frac{16}{24\cdot28}+...+\frac{16}{76\cdot80}\)

\(A=4\cdot\left(\frac{4}{20\cdot24}+\frac{4}{24\cdot28}+...+\frac{4}{76\cdot80}\right)\)(thầy cô trên trường minh dạy sao thì mik làm vậy nha bạn !! =)))

\(A=4\cdot\left(\frac{1}{20}-\frac{1}{24}+\frac{1}{24}-\frac{1}{26}+...+\frac{1}{76}-\frac{1}{80}\right)\)(cứ như thế sẽ cs 2 số trùng rồi lượt còn số đầu vs số cuối nha bạn)

\(A=4\cdot\left(\frac{1}{20}-\frac{1}{80}\right)=4\cdot\left(\frac{4}{80}-\frac{1}{80}\right)=4\cdot\frac{3}{80}=\frac{3}{20}\)

Answer 6

\(A=\frac{16}{20.24}+\frac{16}{24.28}+\frac{16}{28.32}+...+\frac{16}{76.80}\)

\(A=4.\left(\frac{4}{20.24}+\frac{4}{24.28}+\frac{4}{28.32}+...+\frac{4}{76.80}\right)\)

\(A=4.\left(\frac{1}{20}-\frac{1}{24}+\frac{1}{24}-\frac{1}{28}+\frac{1}{28}-\frac{1}{32}+...+\frac{1}{76}-\frac{1}{80}\right)\)

\(A=4.\left(\frac{1}{20}-\frac{1}{80}\right)\)

\(A=4.\frac{3}{80}\)

\(A=\frac{3}{20}\)

Answer 7

 Ta sẽ tính A theo cách thông dụng và dễ kiếm điểm tối đa như sau :

Giải

Ta có : \(A=\frac{16}{20.24}+\frac{16}{24.28}+\frac{16}{28.32}+...+\frac{16}{76.80}\)

\(\Rightarrow A=16.\left(\frac{1}{20.24}+\frac{1}{24.28}+\frac{1}{28.32}+...+\frac{1}{76.80}\right)\)

\(\Rightarrow4A=16.\left(\frac{4}{20.24}+\frac{4}{24.28}+\frac{4}{28.32}+...+\frac{4}{76.80}\right)\)

\(\Rightarrow A=4.\left(\frac{1}{20}-\frac{1}{24}+\frac{1}{24}-\frac{1}{28}+\frac{1}{28}-\frac{1}{32}+...+\frac{1}{76}-\frac{1}{80}\right)\)

\(\Rightarrow A=4.\left(\frac{1}{20}-\frac{1}{80}\right)\)

\(\Rightarrow A=4.\frac{3}{80}\)

\(\Rightarrow A=\frac{3}{20}\)

Vậy \(\Rightarrow A=\frac{3}{20}\)

Chúc cậu luôn học tốt nhé !