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3 tháng 12 2019
\(a.=5-3+12-4-16\)
\(=-2\)
\(b.=-6-\left(-12\right)+7-10\)
\(=6+7-10\)
\(=3\)
S
23 tháng 2 2019
a) \(\frac{5}{12}-\frac{3}{-16}+\frac{3}{4}\)
\(=\frac{5}{12}-\left(-\frac{3}{16}\right)+\frac{3}{4}\)
\(=\frac{5}{12}+\frac{3}{6}+\frac{3}{4}\)
\(=\frac{20+9+36}{48}\)
\(=\frac{65}{48}\)
Mấy câu kia lát làm :))
CH
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Nguyễn Ngọc Anh Minh
CTVHS
VIP
29 tháng 4 2016
a/ \(=\frac{21}{23}+\frac{125}{143}-\frac{101.21}{101.23}-\frac{1001.125}{1001.143}=0\)
b/ \(=\frac{4}{20}+\frac{8}{21}+\frac{2}{5}-\frac{3}{5}+\frac{2}{21}-\frac{10}{21}+\frac{3}{20}=\frac{7}{20}-\frac{1}{5}=\frac{4}{20}\)
c/ \(\frac{C}{2}=\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{420}=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{20.21}\)
\(\frac{C}{2}=\frac{3-2}{2.3}+\frac{4-3}{3.4}+\frac{5-4}{4.5}+...+\frac{21-20}{20.21}=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{20}-\frac{1}{21}\)
\(\frac{C}{2}=\frac{1}{2}-\frac{1}{21}=\frac{19}{42}\Rightarrow C=\frac{19}{21}\)
27 tháng 4 2020
\(A=-\frac{7}{21}+\left(1+\frac{1}{3}\right)\)
\(A=-\frac{1}{3}+1+\frac{1}{3}\)
\(A=\left(-\frac{1}{3}+\frac{1}{3}\right)+1=0+1=1\)
\(B=\frac{2}{15}+\left(\frac{5}{9}+\frac{-6}{9}\right)\)
\(B=\frac{2}{15}+\frac{-1}{9}=\frac{6}{45}+\frac{-5}{45}=\frac{1}{45}\)
\(C=\frac{4}{20}+\frac{16}{42}+\frac{6}{15}+\left(-\frac{3}{5}\right)+\frac{2}{21}+\left(-\frac{10}{21}\right)+\frac{3}{20}\)
\(C=\frac{1}{5}+\frac{8}{21}+\frac{2}{5}+\left(-\frac{3}{5}\right)+\frac{2}{21}+\left(-\frac{10}{21}\right)+\frac{3}{20}\)
\(C=\left(\frac{1}{5}+\frac{2}{5}+\frac{-3}{5}\right)+\left(\frac{8}{21}+\frac{2}{21}+\frac{-10}{21}\right)+\frac{3}{20}\)
\(C=0+0+\frac{3}{20}=\frac{3}{20}\)
5 tháng 6 2018
Bài 1:
a) \(\frac{16}{15}.\frac{\left(-5\right)}{14}.\frac{54}{24}.\frac{56}{21}\)
\(=\frac{4.2.2}{5.3}.\frac{\left(-5\right)}{2.7}.\frac{3.3}{4}.\frac{8}{3}\)
\(=\frac{4.2.2.\left(-5\right).3.3.8}{5.3.2.7.4.3}\)
\(=\frac{-16}{7}\)
b) \(\frac{7}{3}.\frac{\left(-5\right)}{2}.\frac{15}{21}.\frac{4}{\left(-5\right)}\)
\(=\frac{7}{3}.\frac{\left(-5\right)}{2}.\frac{5}{7}.\frac{2.2}{\left(-5\right)}\)
\(=\frac{7.\left(-5\right).5.2.2}{3.2.7.\left(-5\right)}\)
\(=\frac{10}{3}\)
5 tháng 6 2018
Bài 2:
a) \(\frac{21}{24}.\frac{11}{9}.\frac{5}{7}=\frac{7}{8}.\frac{11}{9}.\frac{5}{7}=\frac{11.5}{8.9}=\frac{55}{72}\)
b) \(\frac{5}{23}.\frac{17}{26}+\frac{5}{23}.\frac{9}{26}\)
\(=\frac{5}{23}.\left(\frac{17}{26}+\frac{9}{26}\right)=\frac{5}{23}.1=\frac{5}{23}\)
c) \(\left(\frac{3}{29}-\frac{1}{5}\right).\frac{29}{3}=\frac{3}{29}.\frac{29}{3}-\frac{1}{5}.\frac{29}{3}\)
\(=1-1\frac{14}{15}=\frac{14}{15}\)
Bài 3:
a) x/5 = 2/5
=> x =2
b) -4/x = 20/14 = 10/7
=> -4/x = 10/7
=> x.10 = (-4).7
x.10 = - 28
x= -28 :10
x= -2,8
c) 4/7 = 12/x = 12/ 21
=> 12/x = 12/21
=> x = 21
d) 3/7 = x / 21 = 9/21
=> x/21 = 9/21
=> x= 9
a) 21 . (- 3) = - (21 . 3) = - 63
b) (- 16 ) . 5 = - (16 . 5) = - 80
c) 12 . 20 = 240 d) (- 21) . (- 6) = 126
a) 21 . (- 3) = - (21 . 3) = - 63
b) (- 16 ) . 5 = - (16 . 5) = - 80
c) 12 . 20 = 240
d) (- 21) . (- 6) = 126