Rút gọn các phân số sau:
\(\frac{{12}}{{ - 24}}\); \(\frac{{ - 39}}{{75}}\); \(\frac{{132}}{{ - 264}}\).
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Ta có:
\(\begin{array}{l}\frac{{24}}{{108}} = \frac{{24:12}}{{108:12}} = \frac{2}{9};\\\frac{{80}}{{32}} = \frac{{80:16}}{{32:16}} = \frac{5}{2}\end{array}\)
a ) − 12 − 24 = ( − 12 ) : ( − 12 ) ( − 24 ) : ( − 12 ) = 1 2
b ) 54 270 = 54 : 54 270 : 54 = 1 5
c ) − 12 − 28 = ( − 12 ) : ( − 4 ) ( − 28 ) : ( − 4 ) = 3 7
c ) − 5 15 = ( − 5 ) : 5 15 : 5 = − 1 2 d ) − 12 − 24 = ( − 12 ) : ( − 12 ) ( − 24 ) : ( − 12 ) = 1 2
e ) 54 270 = 54 : 54 270 : 54 = 1 5 f ) − 12 − 28 = ( − 12 ) : ( − 4 ) ( − 28 ) : ( − 4 ) = 3 7
g ) − 18 − 27 = ( − 18 ) : ( − 9 ) ( − 27 ) : ( − 9 ) = 2 3 h ) 45 − 24 = 45 : ( − 3 ) ( − 24 ) : ( − 3 ) = − 15 8
Theo thứ tự : 5/6 ; 2/3 ; 2/3 ; 3/2 ; 2/3 ; 3/8 ; 3/1(hay là 3)
\(\dfrac{10}{12}=\dfrac{5}{6}\) \(\dfrac{8}{12}=\dfrac{2}{3}\) \(\dfrac{10}{15}=\dfrac{2}{3}\) \(\dfrac{27}{18}=\dfrac{3}{2}\) \(\dfrac{24}{36}=\dfrac{4}{6}=\dfrac{2}{3}\)
\(\dfrac{18}{48}=\dfrac{3}{8}\) \(\dfrac{42}{14}=\dfrac{6}{2}=\dfrac{3}{1}\)
Bài 1. Rút gọn các phân số:
24/36 =2/3
12/81=4/27
125/250 =1/2
131313/151515=13/15
20052005/20062006= 2005/2006
Bài 2: So sánh các phân số sau;
3/8 và 1/3
Ta có: 3/8 = 9/24 ; 1/3 = 8/24
=> 3/8 > 1/3
2/5 và 4/7
Ta có: 2/5 = 14/35 ; 4/7 = 20/35
=> 2/5 < 4/7
2004/2005 và 2005/2006
Ta có: 2004/2005 = 1 - 2004/2005 = 1/2005
2005/2006 = 1 - 2005/2006 = 1/2006
=> 2004/2005 < 2005/2006
Bài 4 Tim y biết:
y : 2 + y + y : 3 + y : 4 = 25
=> y : 2 + y : 1 + y : 3 + y : 4 = 25
=> y : (2+1+3+4)=25
=> y : 10 = 25
=> y = 25 x 10
=> y = 250
Vậy y=250
\(\frac{24-12.13}{12+4.9}=\frac{24-156}{12+36}=\frac{-132}{48}=\frac{-11}{4}\)
Rút gọn phân số:
\(\frac{24-12.13}{12+4.9}=\frac{24-4.3.13}{12+4.9}=\frac{24-3.13}{12+9}=\frac{24-3.13}{12+3.3}=\frac{24-13}{12+3}=\frac{11}{14}\)
Sai thì thôi nhé!
\(\frac{24-12.13}{12+4.9}\)=\(\frac{24-156}{12+36}\)=\(\frac{-132}{48}\)=-\(\frac{11}{4}\)
\(\dfrac{1}{3}-\dfrac{1}{5}=\dfrac{5}{15}-\dfrac{3}{15}=\dfrac{2}{15}\)
\(\dfrac{6}{7}-\dfrac{4}{9}=\dfrac{54}{63}-\dfrac{28}{63}=\dfrac{26}{63}\)
Ta có: \(\frac{{12}}{{ - 24}} = \frac{{12:12}}{{ - 24:12}} = \frac{1}{{ - 2}}\)
\(\frac{{ - 39}}{{75}} = \frac{{ - 39:3}}{{75:3}} = \frac{{ - 13}}{{25}}\)
\(\frac{{132}}{{ - 264}} = \frac{{132:132}}{{ - 264:132}} = \frac{1}{{ - 2}}\).