So sánh phân số
a,A=\(\frac{1\cdot1!+2\cdot2!+3\cdot3!+.....+100\cdot100!}{1\cdot199+2\cdot197+3\cdot195+.....+100\cdot1}\)với B = \(\frac{99!}{33}\)
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#It's the moment when you're in good mood, you accidentally click back =.=
1) Calculate
\(P=1\frac{1}{3}.1\frac{1}{8}.1\frac{1}{15}....1\frac{1}{63}.1\frac{1}{80}\)
\(=\frac{4}{3}.\frac{9}{8}.\frac{16}{15}....\frac{64}{63}.\frac{81}{80}\)
\(=\frac{2.2}{1.3}.\frac{3.3}{2.4}.\frac{4.4}{3.5}....\frac{8.8}{7.9}.\frac{9.9}{8.10}\)
\(=\frac{2.9}{10}=\frac{9}{5}\)
ta có: 10010 + 1 > 10010 - 1
⇒ A = \(\frac{100^{10}+1}{100^{10}-1}< \frac{100^{10}+1-2}{100^{10}-1-2}=\frac{100^{10}-1}{100^{10}-3}=B\)
vậy A < B
Gọi A=\(\frac{1}{100.99}-\frac{1}{99.98}-...-\frac{1}{3.2}-\frac{1}{2.1}\)
A= -(\(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{98.99}+\frac{1}{99.100}\))
A=-(1-\(\frac{1}{100}\))
A=-(\(\frac{99}{100}\))
A=-99/100
\(\frac{1}{100.99}-\frac{1}{99.98}-...-\frac{1}{3.2}-\frac{1}{2.1}\)
\(\Leftrightarrow-\left(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{98.99}+\frac{1}{99.100}\right)\)
\(\Leftrightarrow\)\(-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\right)\)
\(\Leftrightarrow-\left(1-\frac{1}{100}\right)\)
\(\Leftrightarrow-\left(\frac{99}{100}\right)\)
\(=-\frac{99}{100}\)
bài này dễ lắm,mình giải đây:
C = \(\frac{1}{100}\)- \(\frac{1}{100.99}\)-\(\frac{1}{99.98}\)\(\frac{1}{98.97}\)- ... - \(\frac{1}{3.2}\)- \(\frac{1}{2.1}\)
C = \(\frac{-1}{1.2}\)+ \(\frac{-1}{2.3}\) + ... +\(\frac{-1}{98.99}\)+ \(\frac{1}{99.100}\)+ \(\frac{1}{100}\)
C = \(\frac{-1}{1}\)- \(\frac{-1}{2}\)
Mình bận rồi , phần sau tự làm nha.