Question

[Rhider]

Giups em zai mình nha 

Bài 1: Không quy đồng hãy tính hợp lý.

a) A=\(\frac{-1}{20}\)+ \(\frac{-1}{30}\)+ \(\frac{-1}{42}\)+ \(\frac{-1}{56}\)+ \(\frac{-1}{72}\)+ \(\frac{-1}{90}\)

b) B=\(\frac{5}{2.1}\)+ \(\frac{4}{1.11}\)+ \(\frac{3}{11.2}\)+ \(\frac{1}{2.15}\)+ \(\frac{13}{15.4}\)

Bài 2: Không tính giá trị hãy so sánh.

a) \(\frac{1717}{8585}\)và \(\frac{1313}{5151}\)                             b)\(\frac{201201}{202202}\)và \(\frac{201201201}{202202202}\)

Answer 1

[ILoveMath]

\(a,\Rightarrow A=-1\left(\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+...+\dfrac{1}{9.10}\right)\)

\(\Rightarrow A=-1\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+...+\dfrac{1}{9}-\dfrac{1}{10}\right)\)

\(\Rightarrow A=-1\left(\dfrac{1}{4}-\dfrac{1}{10}\right)\)

\(\Rightarrow A=\dfrac{-3}{20}\)

Answer 2

[Nguyễn Hoàng Minh]

Bài 2:

\(a,\dfrac{1717}{8585}=\dfrac{1717:1717}{8585:1717}=\dfrac{1}{5};\dfrac{1313}{5151}=\dfrac{1313:101}{5151:101}=\dfrac{13}{51}\\ \dfrac{1}{5}=\dfrac{51}{255}< \dfrac{65}{255}=\dfrac{13}{51}\\ \Rightarrow\dfrac{1717}{8585}< \dfrac{1313}{5151}\)

\(b,\dfrac{201201}{202202}=\dfrac{201201:1001}{202202:1001}=\dfrac{201}{202}=\dfrac{201\cdot1001001}{202\cdot1001001}=\dfrac{201201201}{202202202}\)