15/25-3/21 =?
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
1)
S1=(1+999)+(2+998)+...+(501+499)+500
S1=1000.(999-1)+500
S1=998 000 + 500
S1=998 500
:/ câu 1 quá ez mik bik làm rồi còn các câu sau nó thì mik chịu
![](https://rs.olm.vn/images/avt/0.png?1311)
2/14+3/21=1/7+1/7=2/7
4/5+15/25=4/5+3/5=7/5
21/27+4/9=7/9+4/9=11/9
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(\dfrac{7}{-25}+\dfrac{8}{25}=\dfrac{-7}{25}+\dfrac{8}{25}=\dfrac{1}{25}\)
\(\dfrac{4}{5}+\dfrac{4}{-18}=\dfrac{4}{5+\left(-18\right)}=\dfrac{4}{-13}=\dfrac{-4}{13}\)
\(\dfrac{7}{21}+\dfrac{9}{-36}=\dfrac{1}{3}+\dfrac{1}{-4}=\dfrac{1}{3+\left(-4\right)}=\dfrac{1}{-1}=1\)
b) \(\dfrac{12}{20}-\dfrac{2}{5}=\dfrac{12}{20}+\left(\dfrac{-2}{5}\right)=\dfrac{3}{5}+\dfrac{-2}{5}=\dfrac{3+\left(-2\right)}{5}=\dfrac{1}{5}\)
\(\dfrac{2}{3}-\dfrac{-5}{6}=\dfrac{2}{3}+\dfrac{5}{6}=\dfrac{4}{6}+\dfrac{5}{6}=\dfrac{9}{6}=\dfrac{3}{2}\)
\(6-\dfrac{3}{20}=6+\dfrac{-3}{20}=\dfrac{60}{60}+\dfrac{-9}{60}=\dfrac{51}{60}\)
c) \(\dfrac{2}{21}.\dfrac{-7}{3}=\dfrac{2.\left(-1\right)}{7.3}=\dfrac{-2}{21}\)
\(\dfrac{27}{28}.\left(-21\right)=\dfrac{27.\left(-21\right)}{28}=\dfrac{-567}{28}\)
\(\dfrac{-15}{7}.\dfrac{-14}{25}=\dfrac{-3.\left(-2\right)}{1.5}=\dfrac{6}{5}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{7}{21}+\dfrac{17}{25}-\dfrac{20}{15}+\dfrac{3}{4}+\dfrac{8}{25}\)
\(=\dfrac{1}{3}+\dfrac{17}{25}-\dfrac{4}{3}+\dfrac{3}{4}+\dfrac{8}{25}\)
\(=\left(\dfrac{1}{3}-\dfrac{4}{3}\right)+\left(\dfrac{17}{25}+\dfrac{8}{25}\right)+\dfrac{3}{4}\)
\(=-1+1+\dfrac{3}{4}\)
\(=\dfrac{3}{4}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
1/3 + 7/5 = 26/15
3/15 + 2/5 = 3/5
4/6 + 18/27 = 4/3
15/25 + 6/21 = 31/35
k nhé:))
\(\frac{1}{3}\)+\(\frac{7}{5}\)=\(\frac{5}{15}\)+\(\frac{21}{15}\)=\(\frac{26}{15}\)
\(\frac{3}{15}\)+\(\frac{2}{5}\)=\(\frac{1}{5}\)+\(\frac{2}{5}\)=\(\frac{3}{5}\)
\(\frac{4}{6}\)+\(\frac{18}{27}\)=\(\frac{2}{3}\)+\(\frac{2}{3}\)=\(\frac{4}{3}\)
\(\frac{15}{25}\)+\(\frac{6}{21}\)=\(\frac{3}{5}\)+\(\frac{2}{7}\)=\(\frac{21}{35}\)+\(\frac{10}{35}\)=\(\frac{31}{35}\)
đây nha
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(3-\dfrac{5}{3}=\dfrac{1}{3};\dfrac{15}{7}-2=\dfrac{1}{7}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(1,=38-42+14-25+27+15=27\)
\(2,=12+21-23+21-10=21\)
\(3,=57-725-605+53=-1220\)
\(4,=55+45+15-15+55-45=110\)
![](https://rs.olm.vn/images/avt/0.png?1311)
` 1, 5 . ( -2/25 = 3/2 . (-2)/25 = -6/50 = -3/25 `
` 1 3/5 . (-3)/4 = 8/5 . (-3)/4 = -24/20 = -6/5 `
`-15/4 : 21/(-1) = -15/4 . (-1)/21 = 15/84 = 5/28 `
` ( -2 1/7 ) : ( -1 1/14 ) = (-15)/7 : (-15)/14 = -15/7 . (-14)/15 = 210/105 = 2 `
`@animephamdanhv.`
\(\frac{15}{25}-\frac{3}{21}\)
\(=\frac{3}{5}-\frac{1}{7}\)
\(=\frac{21}{35}-\frac{5}{35}=\frac{16}{35}\)
\(\frac{15}{25}-\frac{3}{21}\)
\(=\frac{3}{5}-\frac{1}{7}\)
\(=\frac{21}{35}-\frac{5}{35}\)
\(=\frac{16}{35}\)
HT