a: 13/15=1-2/15
23/25=1-2/25
mà 2/15>2/25
nên 13/15<23/25
b: 23/28=621/756
24/27=672/756
mà 621<672
nên 23/28<24/27
c: \(\dfrac{12}{25}=\dfrac{588}{1225}\)
\(\dfrac{25}{49}=\dfrac{625}{1225}\)
mà 588<625
nên 12/25<25/49
\(\dfrac{13}{15};\dfrac{23}{25}=MSC:375=\dfrac{325}{375}< \dfrac{345}{375}\)
\(\dfrac{23}{28};\dfrac{24}{27}=MSC:756=\dfrac{621}{756}< \dfrac{672}{756}\)
\(\dfrac{12}{25};\dfrac{25}{49}=MSC:1225=\dfrac{588}{1225}< \dfrac{625}{1225}\)
\(\dfrac{13}{15};\dfrac{133}{153}=MSC:2295=\dfrac{1989}{1195}< \dfrac{1995}{1195}\)
`a)13/15 = 1 - 2/15`
`23/25 = 1 - 2/25`
Vì `2/15 > 2/25`
`=> 1- 2/15 < 1 - 2/25 <=> 13/15 < 23/25`
__________________________________________
`b) 23/28 và 24/27`
ta có :
`23/28 = (23xx27)/(28xx27) = 621/756`
`24/27 = (24 xx 28)/(27xx28) = 672/756`
Vì `621/756 < 672/756 <=> 23/28 < 24/27`
__________________________________________
`12/25` và `25/49`
ta có :
`12/25 = (12 xx 49)/(25 xx 49) = 588/1225`
`25/49 = (25 xx 25)/(49 xx 25)= 625/1225`
vì `588/1225<625/1225 <=> 12/25 < 25/49`
__________________________________________
`13/15` và `133/153`
ta có :
`13/15 = (13 xx 153)/(15 xx 153) = 1989/2295`
`133/153 = (133xx15)/(153xx15) = 1995/2295`
Vì`1989/2295 < 1995/2295 <=> 13/15 < 133/153`