Ta có: \(\frac{13}{15}=\frac{130}{150}=1-\frac{20}{150}\)

và \(\frac{133}{155}=1-\frac{20}{155}\)

Vì \(\frac{20}{150}>\frac{20}{155}\)nên \(1-\frac{20}{150}< 1-\frac{20}{155}\)

hay \(\frac{13}{15}< \frac{133}{155}\)

\(\frac{13}{15}>\frac{133}{155}\)

trong sách toán 5 trang so sánh phân số có mà,bạn mở ra xem đi

trang mấy đó bạn

\(\frac{13}{15}=\frac{13.133}{15.133}\)\(=\frac{1729}{1995}\)

\(\frac{133}{155}\)\(=\frac{133.13}{155.13}\)\(=\frac{1729}{2015}\)

Vì: \(\frac{1729}{1995}\)>\(\frac{1729}{2015}\)nên \(\frac{13}{15}\)>\(\frac{133}{155}\)

12/25 < 25/49

13/15 > 133/155

theo mình là bằng nhau

\(\frac{13}{25}< \frac{133}{153}\)

\(\frac{13}{15}>\frac{1333}{1555}\)

mk nha nhất

\(\frac{13}{25}< \frac{133}{153}\)

\(\frac{13}{15}>\frac{1333}{1555}\)

a)Có \(\frac{13}{25}=\frac{65}{125};\frac{133}{153}=\frac{399}{459}\)
Có \(1-\frac{65}{125}=\frac{60}{125};1-\frac{399}{459}=\frac{60}{459}\)
Vì \(\frac{60}{125}>\frac{60}{459}\)=) \(1-\frac{65}{125}>1-\frac{399}{459}\)=) \(\frac{65}{125}< \frac{399}{459}\)
=) \(\frac{13}{25}< \frac{133}{153}\)
b) Có \(\frac{13}{15}=\frac{1443}{1665}\)
Có \(1-\frac{1443}{1665}=\frac{222}{1665};1-\frac{1333}{1555}=\frac{222}{1555}\)
Vì \(\frac{222}{1665}< \frac{222}{1555}\)=) \(1-\frac{1443}{1665}< 1-\frac{1333}{1555}\)=) \(\frac{1443}{1665}>\frac{1333}{1555}\)
=) \(\frac{13}{15}>\frac{1333}{1555}\)

13/15>133/155

13/15>1333/1555

tk mk nha mk đang âm điểm

ta thấy gấp tử số và mẫu số 13/15 lên 10 lần thì được 130/150 , 133/155 - 130/150 = 3/5 lúc này ta so sánh

3/5 và 13/15 = 9/15 < 13/15 nên 133/155 < 13/15

và bài kia cũng như vậy bạn nha ^ ^

Ai tháy đúng k mình nhé ^D^

Bài 1:

Ta có:

\(\left(\frac{1}{10}\right)^{15}=\left(\frac{1}{5}\right)^{3.5}=\left(\frac{1}{125}\right)^5\)

\(\left(\frac{3}{10}\right)^{20}=\left(\frac{3}{10}\right)^{4.5}=\left(\frac{81}{10000}\right)^5\)

Lại có:

\(\frac{1}{125}=\frac{80}{10000}< \frac{81}{10000}\Rightarrow\left(\frac{1}{125}\right)^5< \left(\frac{81}{10000}\right)^5\)

\(\Rightarrow\left(\frac{1}{10}\right)^{15}< \left(\frac{3}{10}\right)^{20}\)

Bài 2:

Ta có:

\(A=\frac{13^{15}+1}{13^{16}+1}\Rightarrow13A=\frac{13^{16}+13}{13^{16}+1}=1+\frac{12}{13^{16}+1}\)

\(B=\frac{13^{16}+1}{13^{17}+1}\Rightarrow13B=\frac{13^{17}+13}{13^{17}+1}=1+\frac{12}{13^{17}+1}\)

Mà \(\frac{12}{13^{16}+1}>\frac{12}{13^{17}+1}\)

\(\Rightarrow1+\frac{12}{13^{16}+1}>1+\frac{12}{13^{17}+1}\)

\(\Rightarrow13A>13B\Rightarrow A>B\)

\(S=\frac{1}{11}+\frac{1}{12}+\frac{1}{13}+\frac{1}{14}+....+\frac{1}{20}\)

\(=\left(\frac{1}{11}+\frac{1}{12}+\frac{1}{13}+\frac{1}{14}+\frac{1}{15}\right)+\left(\frac{1}{16}+\frac{1}{17}+\frac{1}{18}+\frac{1}{19}+\frac{1}{20}\right)\)

\(>\frac{1}{15}\cdot5+\frac{1}{20}\cdot5\)

\(=\frac{1}{3}+\frac{1}{4}\)

\(=\frac{7}{12}>\frac{6}{12}=\frac{1}{2}\)

\(\Rightarrow S>\frac{1}{2}\)

Bài làm

Ta có: 

\(\frac{1}{11}>\frac{1}{20}\), \(\frac{1}{12}>\frac{1}{20}\), \(\frac{1}{13}>\frac{1}{20}\), \(\frac{1}{14}>\frac{1}{20}\), \(\frac{1}{15}>\frac{1}{20}\), \(\frac{1}{16}>\frac{1}{20}\), \(\frac{1}{17}>\frac{1}{20}\), \(\frac{1}{18}>\frac{1}{20}\),\(\frac{1}{19}>\frac{1}{20}\)

=> \(S=\frac{1}{11}+\frac{1}{12}+\frac{1}{13}+\frac{1}{14}+\frac{1}{15}+\frac{1}{16}+\frac{1}{17}+\frac{1}{18}+\frac{1}{19}+\frac{1}{20}>\frac{1}{20}\)

hay \(\frac{1}{20}+\frac{1}{20}+\frac{1}{20}+\frac{1}{20}+\frac{1}{20}+\frac{1}{20}+\frac{1}{20}+\frac{1}{20}+\frac{1}{20}+\frac{1}{20}\)

=> \(S=\frac{1}{20}.10=\frac{10}{20}=\frac{1}{2}\)

Do đó: \(S=\frac{1}{2}\)

# Chúc bạn học tốt #

Ta có các phân số : \(\frac{1}{11};\frac{1}{12};\frac{1}{13};\frac{1}{14};\frac{1}{15};\frac{1}{16};\frac{1}{17};\frac{1}{18};\frac{1}{19}>\frac{1}{20}\)

Do đó : \(\frac{1}{11}+\frac{1}{12}+\frac{1}{13}+\frac{1}{14}+\frac{1}{15}+\frac{1}{16}+\frac{1}{17}+\frac{1}{18}+\frac{1}{19}+\frac{1}{20}>\frac{1}{20}+\frac{1}{20}+...+\frac{1}{20}\)có 10 phân số \(\frac{1}{20}\)

\(\frac{1}{11}+\frac{1}{12}+\frac{1}{13}+\frac{1}{14}+\frac{1}{15}+\frac{1}{16}+\frac{1}{17}+\frac{1}{18}+\frac{1}{19}+\frac{1}{20}>\frac{10}{20}\)

\(\frac{1}{11}+\frac{1}{12}+\frac{1}{13}+\frac{1}{14}+\frac{1}{15}+\frac{1}{16}+\frac{1}{17}+\frac{1}{18}+\frac{1}{19}+\frac{1}{20}>\frac{1}{2}\)

Vậy : \(S>\frac{1}{2}\)