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a: =-21/36-3/36=-24/36=-2/3
b: =43/12*1/2+5/24=43/24+5/24=2
c: =8/9+1/9=1
e: =1-1/4+1/4-1/7+...+1/97-1/100
=1-1/100=99/100
a. \(\left(\dfrac{-2}{7}+\dfrac{4}{7}\right)+\dfrac{1}{7}=\dfrac{2}{7}+\dfrac{1}{7}=\dfrac{3}{7}\)
b. \(\left(\dfrac{-8}{19}+\dfrac{27}{19}\right)+\left(\dfrac{-4}{21}+\dfrac{-17}{21}\right)+\dfrac{-12}{16}=\dfrac{19}{19}+\dfrac{-21}{21}+\dfrac{-12}{16}\)
\(=1+\left(-1\right)+\dfrac{-12}{16}=\dfrac{-12}{16}\)
c. \(\dfrac{-3}{7}+\dfrac{-11}{13}+\dfrac{-2}{13}+\dfrac{3}{7}+1=\left(\dfrac{-3}{7}+\dfrac{3}{7}\right)+\left(\dfrac{-11}{13}+\dfrac{-2}{13}\right)+1=0-1+1=0\)
-2/7 + 2/7 : 3/5
= -2/7 + 2/7. 3/5
= -2/7 + 35/6
= -12/42 + 245/42
= -233/42
−819+−421−1721+271919−8+21−4−2117+1927
= (-4/21 - 17/21) + (-8/19 + 27/19)
= - 13/21 + -19/19
= (-13/21)+ (-1)
= (-13/21) + (-1/1)
= (-13/21) + (-13/21)
= - 26/21
65.313−65.161356.133−56.1316
=6/5. (3/13 - 16/13)
= 6/5. (-13/13)
=6/5. (-1)
=6/5. (-1/1)
=6/5. (-6/5)
=(-36/25)
Tính hợp lí:
a) \(\left(-0,4\right)+\dfrac{3}{8}+\left(-0,6\right)\)
\(=\left[\left(-0,4\right)+\left(-0,6\right)\right]+\dfrac{3}{8}\)
\(=-1+\dfrac{3}{8}\)
\(=\dfrac{\left(-8\right)+3}{8}\)
\(=\dfrac{-5}{8}\)
b) \(\dfrac{4}{5}-1,8+0,375+\dfrac{5}{8}\)
\(=\dfrac{4}{5}-\dfrac{9}{5}+\dfrac{3}{8}+\dfrac{5}{8}\)
\(=-1+1\)
\(=0\\\)
c) \(\dfrac{7}{3}.\left(-2,5\right).\dfrac{6}{7}\)
\(=\dfrac{7}{3}.\dfrac{-5}{2}.\dfrac{6}{7}\)
\(=\dfrac{7}{3}.\dfrac{6}{7}.\dfrac{-5}{2}\)
\(=2.\dfrac{-5}{2}\)
\(=-5\)
d) \(\dfrac{7}{12}.\left(-2,34\right)-\dfrac{7}{12}.\left(-0,34\right)\)
\(=\dfrac{7}{12}.\left[\left(-2,34\right)+0,34\right]\)
\(=\dfrac{7}{12}.\left(-2\right)\)
\(=\dfrac{-7}{6}\)
e) \(\dfrac{-8}{3}.\dfrac{2}{11}-\dfrac{8}{3}:\dfrac{11}{9}\)
\(=\dfrac{8}{3}.\dfrac{-2}{11}-\dfrac{8}{3}.\dfrac{9}{11}\)
\(=\dfrac{8}{3}.\left(\dfrac{-2}{11}-\dfrac{9}{11}\right)\)
\(=\dfrac{8}{3}.-1\)
\(=\dfrac{-8}{3}\)
Chúc bạn học tốt
2:
a: =>x=1/2+1/6=3/6+1/6=4/6=2/3
b: =>x+3,5=7,8-6,3=1,5
=>x=1,5-3,5=-2
c: =>(35-x)/-105=1/5
=>35-x=-21
=>x=56
1
c hình như tính bình thường thôi:v
d
= 1,75 : 5 + 2,5 . (16 – 4 . 4,1)
= 1,75 : 5 + 2,5 . (16 – 16,4)
= 1,75 : 5 + 2,5 . (−0,4)
= 0,35 − 1
= −0,65.
2
a
\(\Rightarrow x=\dfrac{1}{2}+\dfrac{1}{6}=\dfrac{3}{6}+\dfrac{1}{6}=\dfrac{4}{6}=\dfrac{2}{3}\)
b
\(\Rightarrow x+\dfrac{35}{10}=\dfrac{78}{10}-\dfrac{63}{5}:2\\ \Rightarrow x+\dfrac{35}{10}=\dfrac{78}{10}-\dfrac{63}{10}=\dfrac{15}{10}\\ \Rightarrow x=\dfrac{15}{10}-\dfrac{35}{10}=-2\)
c không rõ đề:v
Gợi ý: Sử dụng tính chất phân phối của phép nhân đối với phép cộng để nhóm thừa số chung ra ngoài.
a ) 4 - \(1\dfrac{4}{5}\).\(\dfrac{-3}{4}\) = 4 - \(\dfrac{-3}{5}\)= \(\dfrac{23}{5}\)
b) \(\dfrac{1}{7}.2\dfrac{1}{3}+\dfrac{5}{2}:\dfrac{3}{7}-\dfrac{59}{6}.\dfrac{1}{7}\)
\(\dfrac{1}{7}.\dfrac{7}{3}+\dfrac{5}{2}:\dfrac{3}{7}-\dfrac{59}{6}\cdot\dfrac{1}{7}\)
\(\dfrac{1}{7}\cdot\left(\dfrac{7}{3}-\dfrac{59}{6}\right)+\dfrac{35}{6}\)
\(\dfrac{1}{7}\cdot\dfrac{-15}{2}+\dfrac{35}{6}=\dfrac{-15}{14}+\dfrac{35}{6}=\dfrac{100}{21}\)
\(a,4-1\dfrac{5}{7}.\left(-0,75\right)\) = \(4-\dfrac{12}{7}.\dfrac{-75}{100}\) = \(4-\dfrac{12}{7}.\dfrac{3}{4}\)
=\(4-\dfrac{36}{28}=4-\dfrac{9}{7}=\dfrac{28}{7}-\dfrac{9}{7}=\dfrac{19}{7}\)
b, \(\dfrac{1}{7}.2\dfrac{1}{3}+\dfrac{5}{2}:\dfrac{3}{7}-\dfrac{59}{6}.\dfrac{1}{7}\) \(=\dfrac{1}{7}.\dfrac{7}{3}+\dfrac{5}{2}.\dfrac{7}{3}-\dfrac{59}{6}.\dfrac{1}{7}=\dfrac{7}{3}.\left(\dfrac{1}{7}+\dfrac{5}{2}\right)-\dfrac{59}{6}.\dfrac{1}{7}\)
=\(\dfrac{7}{3}.\left(\dfrac{2}{14}+\dfrac{35}{14}\right)-\dfrac{59}{42}=\dfrac{7}{3}.\dfrac{37}{14}-\dfrac{59}{42}\)
= \(\dfrac{1.37}{3.2}-\dfrac{59}{42}=\dfrac{37}{6}-\dfrac{59}{42}=\dfrac{259}{42}-\dfrac{59}{42}=\dfrac{200}{42}=\dfrac{100}{21}\)
a, A = (2,34 + 7,66) + (5,35 + 4,65)
A = 10 + 10
A = 20
b, B = 2,13 . (75 + 25)
B = 2,13 . 100
B = 213
c, C = 2/3 - 4/9
C = 2/9
A=\((\)2,34+7,66\()\)+\((\)5,35+4,65\()\)
A=10+10
A=20
B=2,13*\((\)75+65\()\)
B=2,13*140
B=298,2
C=\(\dfrac{2}{3}\)-\(\dfrac{4}{9}\)
C=\(\dfrac{2}{9}\)