Ta có: \(\dfrac{20}{39}>\dfrac{20}{41}>\dfrac{18}{41}\left(1\right)\)
\(\dfrac{22}{27}>\dfrac{22}{29}\left(2\right)\)
\(\dfrac{18}{43}=1-\dfrac{25}{43};\dfrac{14}{39}=1-\dfrac{25}{39}\)
Vì \(\dfrac{25}{43}< \dfrac{25}{39}\Rightarrow1-\dfrac{25}{43}>1-\dfrac{25}{39}\Rightarrow\dfrac{18}{43}>\dfrac{14}{39}\left(3\right)\)
Từ \(\left(1\right);\left(2\right);\left(3\right)\) ta suy ra : A>B
So sánh A và B :
a) \(A=\dfrac{20}{39}+\dfrac{22}{27}+\dfrac{18}{43}\)
\(B=\dfrac{14}{39}+\dfrac{22}{29}+\dfrac{18}{41}\)
b) \(A=\dfrac{3}{8^3}+\dfrac{7}{8^4}\)
\(B=\dfrac{7}{8^3}+\dfrac{3}{8^4}\)
c) \(A=\dfrac{10^7+5}{10^7-8}\)
\(B=\dfrac{10^8+6}{10^8-7}\)
d) \(A=\dfrac{10^{1992}+1}{10^{1991}+1}\)
\(B=\dfrac{10^{1993}+1}{10^{1992}+1}\)
bài 1 : so sánh phân số sau:
a) \(\dfrac{18}{91}\)và\(\dfrac{23}{114}\)
b)\(\dfrac{21}{52}\)và\(\dfrac{213}{523}\)
bài 2:so sánh
a)\(\dfrac{n}{n+1}\)và\(\dfrac{n+2}{n+3}\)
b)\(\dfrac{n}{n+3}\)và\(\dfrac{n-1}{n+4}\)
c)\(\dfrac{n}{2n+1}\)và \(\dfrac{3n+1}{6n+3}\)
bài 3: so sánh A và B
a)\(A=\dfrac{20}{39}+\dfrac{22}{27}+\dfrac{18}{43}\)
\(B=\dfrac{14}{39}+\dfrac{22}{29}+\dfrac{18}{14}\)
b)\(A=\dfrac{10^{1992}+1}{10^{1991}+1}\)
\(B=\dfrac{10^{1993}+1}{10^{1992}+1}\)
c)\(A=\dfrac{10^7+5}{10^7-8}\)
\(B=\dfrac{10^8+6}{10^8-7}\)
So sánh hai phân số: A = 20\39 + 22\27 + 18\43 và B = 14\39 + 22\39 + 18\41.
Rút gọn phân số : 199 .......9 \ 999....... 9.
1 tinh
a,\(5\dfrac{4}{23}.27\dfrac{3}{47}+4\dfrac{3}{47}.\left(-5\dfrac{4}{23}\right)\)
b,4.\(\left(\dfrac{-1}{2}\right)^3+\dfrac{3}{2}\)
c,\(\left(\dfrac{1999}{2011}-\dfrac{2011}{1999}\right)-\left(\dfrac{-12}{1999}-\dfrac{12}{2011}\right)\)
d,\(\left(\dfrac{-5}{11}+\dfrac{7}{22}-\dfrac{-4}{33}-\dfrac{5}{44}\right):\left(\dfrac{381}{22}-39\dfrac{7}{22}\right)\)
\(Tính: B = \dfrac{2 - \dfrac{2}{19} + \dfrac{2}{43} - \dfrac{2}{2017}}{3 - \dfrac{3}{19} + \dfrac{3}{43} - \dfrac{3}{2017}} :\dfrac{4 - \dfrac{4}{29} + \dfrac{4}{41} - \dfrac{4}{2018}}{5 - \dfrac{5}{29} + \dfrac{5}{41} - \dfrac{5}{2018}} \)
\(A=\dfrac{5-\dfrac{5}{29}+\dfrac{5}{41}-\dfrac{5}{2941}}{3-\dfrac{3}{19}+\dfrac{3}{43}-\dfrac{3}{1943}}:\dfrac{4-\dfrac{4}{29}+\dfrac{4}{41}-\dfrac{4}{2941}}{2-\dfrac{2}{19}+\dfrac{2}{43}-\dfrac{2}{1943}}\)
Rút gọn
AI TEACHES ME bài này với:So sánh A và B không qua quy đồng,bieets:A=20/39+22/37+18/43 và B=14/39+22/29+18/41.
bài 1 so sánh
a) \(\dfrac{45}{105}va\dfrac{84}{147}\)
b) \(\dfrac{-12}{19}va\dfrac{-14}{17}\)
c) \(\dfrac{13}{19}va\dfrac{47}{53}\)
d) \(\dfrac{-29}{38}va\dfrac{-13}{22}\)
\(\dfrac{\left(17\dfrac{8}{19}-16\dfrac{9}{18}\right).\left(17,5+16\dfrac{17}{51}-32\dfrac{15}{22}\right)}{\dfrac{7}{3.13}+\dfrac{7}{13.23}+\dfrac{7}{23.33}}\)
