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)\(A=\dfrac{10^7+5}{10^7-8}\)
\(B=\dfrac{10^8+6}{10^8-7}\)
Vì 18/91 < 18/90 =1/5
23/114>23115=1/5
vậy 18/91<1/5<23/114
suy ra 18/91<23/114
vì 21/52=210/520
Mà 210/520=1-310/520
213/523=1-310/523
310/520>310/523
vậy 210/520<213/523
suy ra 21/52<213/523
