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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) \(\dfrac{2}{21}.\dfrac{-7}{3}=\dfrac{2.\left(-1\right)}{7.3}=\dfrac{-2}{21}\)
\(\dfrac{27}{28}.\left(-21\right)=\dfrac{27.\left(-21\right)}{28}=\dfrac{-567}{28}\)
\(\dfrac{-15}{7}.\dfrac{-14}{25}=\dfrac{-3.\left(-2\right)}{1.5}=\dfrac{6}{5}\)
câu 1)
\(\dfrac{-12}{18}+\left(\dfrac{-21}{35}\right)=\dfrac{-19}{15}\)
câu 2)
\(-\dfrac{3}{21}+\dfrac{6}{42}=0\)
câu 3)
\(-\dfrac{18}{24}+\dfrac{15}{21}=-\dfrac{1}{28}\)
câu 4)
\(\dfrac{1}{6}+\dfrac{2}{5}=\dfrac{17}{30}\)
câu 5)
\(\dfrac{3}{5}+\left(-\dfrac{7}{4}\right)=-\dfrac{23}{20}\)
câu 6)
\(\left(-2\right)+\left(\dfrac{-5}{8}\right)=\dfrac{-21}{8}\)
câu 7)
\(\dfrac{1}{-8}+\left(-\dfrac{5}{9}\right)=-\dfrac{49}{72}\)
câu 8)
\(\dfrac{4}{13}+\dfrac{12}{39}=\dfrac{8}{13}\)
câu 9)
\(\dfrac{1}{21}+\dfrac{1}{28}=\dfrac{1}{12}\)
câu 10)
\(-\dfrac{3}{29}+\dfrac{16}{58}=\dfrac{5}{29}\)
câu 11)
\(\dfrac{8}{40}+\left(-\dfrac{36}{45}\right)=-\dfrac{3}{5}\)
câu 12)
\(-\dfrac{8}{18}+\left(-\dfrac{15}{27}\right)=-1\)
câu 13)
\(\dfrac{13}{30}+\left(-\dfrac{1}{5}\right)=\dfrac{7}{30}\)
câu 14)
\(\dfrac{2}{21}+\dfrac{1}{28}=\dfrac{11}{84}\)
câu 15)
\(5+\left(-\dfrac{3}{4}\right)=\dfrac{17}{4}\)
câu 16)
\(\dfrac{18}{24}+\dfrac{45}{-10}=-\dfrac{15}{4}\)
a, \(\frac{21}{30}\) và \(\frac{43}{60}\)
Ta có: \(\frac{21}{30}=\frac{42}{60}\)
Vì \(\frac{42}{60}< \frac{43}{60}\) nên \(\frac{21}{30}< \frac{43}{60}\)
b, \(\frac{-5}{7}\) và \(\frac{-8}{21}\)
Ta có: \(\frac{-5}{7}=\frac{-15}{21}\)
Vì \(\frac{-15}{21}< \frac{-8}{21}\) nên \(\frac{-5}{7}< \frac{-8}{21}\)
c, \(\frac{3}{5}\) và \(\frac{-7}{55^2}\)
Ta có: \(\frac{3}{5}\) > 0; \(\frac{-7}{55^2}\) < 0 nên \(\frac{3}{5}>\frac{-7}{55^2}\)
d, \(\frac{7}{4}\) và \(\frac{5}{6}\)
Vì \(\frac{7}{4}\) > 1; \(\frac{5}{6}\) < 1 nên \(\frac{7}{4}>\frac{5}{6}\)
e, \(\frac{9999}{1000}\) và \(\frac{1000}{9999}\)
Vì \(\frac{9999}{1000}\) > 1 và \(\frac{1000}{9999}\) < 1 nên \(\frac{9999}{1000}>\frac{1000}{9999}\)
f, \(\frac{27}{21}\) và \(\frac{27}{12}\)
Vì 21 > 12 nên \(\frac{27}{21}< \frac{27}{12}\)
Chúc bn học tốt
\(\Leftrightarrow-\dfrac{2}{9}+\dfrac{2}{3}-\dfrac{4}{9}>=x>=\dfrac{3}{7}-\dfrac{7}{5}+\dfrac{11}{7}+\dfrac{2}{5}\)
=>0>=x>=1
=>\(x\in\varnothing\)
a; \(\dfrac{9}{27}\) + \(\dfrac{7}{-49}\)
= \(\dfrac{1}{3}\) - \(\dfrac{1}{7}\)
= \(\dfrac{7}{21}\) - \(\dfrac{3}{21}\)
= \(\dfrac{4}{21}\)
b; - \(\dfrac{12}{10}\) + \(\dfrac{-25}{30}\)
= - \(\dfrac{6}{5}\) - \(\dfrac{5}{6}\)
= -\(\dfrac{36}{30}\) - \(\dfrac{25}{30}\)
= \(\dfrac{-61}{30}\)
c; \(\dfrac{-20}{35}\) + \(\dfrac{-16}{-24}\)
= - \(\dfrac{4}{7}\) + \(\dfrac{2}{3}\)
= - \(\dfrac{12}{21}\) + \(\dfrac{14}{21}\)
= \(\dfrac{2}{21}\)
d; - \(\dfrac{21}{77}\) + \(\dfrac{10}{-35}\)
= - \(\dfrac{3}{11}\) - \(\dfrac{2}{7}\)
= - \(\dfrac{21}{77}\) - \(\dfrac{22}{77}\)
= - \(\dfrac{43}{77}\)
`#` `\text{dkhanhqlv}`
`4)`
`a)3.(-5/11)`
`=-15/11`
`b)3/5+4/7 . 14/6`
`=3/5 + 4/3`
`=9/15+20/15`
`=29/15`
`c) 10/21-3/8 . 4/15`
`=10/21-1/10`
`=100/210-21/210`
`=79/100`
`d)(2/3+3/4)(5/7+5/14)`
`=(8/12+9/12)(10/14+5/14)`
`=17/12 . 15/14`
`=85/56`
`5)`
`a)x-1/2=3/10 . 5/6`
`=>x-1/2=1/4`
`=>x=1/4+1/2`
`=>x=1/4+2/4`
`=>x=3/4`
`b)x/5 = -3/14`
`=>x : 5 = -3/14`
`=>x=-3/14 . 5`
`=>x=-15/14`
`c)x+2/3=9/15 . 5/27`
`=>x+2/3=1/9`
`=>x=1/9-2/3`
`=>x=1/9-6/9`
`=>x=-5/9`
moi nguoi oi giup voi
(-2) + 6 = 4
(-120) + (-60) = -180
| 21 - ( - 7) | + ( - 6)= 23
( - 5) + 21 = 16
( - 70) + ( - 21) = -91
6 + | ( - 7) + ( - 6)| = 19
27 + -( 5) = 22
27 + ( - 5 ) = 22
Đúng thì k còn sai thì thui chứ đừng k sai nhé.