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DA
16 tháng 8 2017
a)\(A=\frac{2}{3}+\frac{2}{6}+\frac{2}{12}+\frac{2}{24}+\frac{2}{48}+\frac{2}{96}+\frac{2}{192}\)
\(\frac{1}{2}xA=\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}+\frac{1}{192}\)
\(\frac{1}{4}xA=\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}+\frac{1}{192}+\frac{1}{384}\)
\(\frac{1}{4}xA-\frac{1}{2}xA=\frac{1}{3}-\frac{1}{384}\)
\(\frac{1}{4}xA=\frac{127}{384}\)
\(A=\frac{127}{384}:\frac{1}{4}\)
\(A=\frac{127}{96}\)
KT
15 tháng 10 2018
\(\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+...+\frac{89}{90}\)
\(=1-\frac{1}{2}+1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+...+1-\frac{1}{90}\)
\(=9-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}\right)\)
\(=9-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}\right)\)
\(=9-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{9}-\frac{1}{10}\right)\)
\(=9-\left(1-\frac{1}{10}\right)\)
\(=9-\frac{9}{10}=\frac{81}{10}\)
30 tháng 7 2023
\(\dfrac{2}{3}\)x\(\dfrac{7}{4}\):\(\dfrac{a}{12}\)=\(\dfrac{2}{3}\)
=>\(\dfrac{7}{6}\):\(\dfrac{a}{12}\)=\(\dfrac{2}{3}\)
=>\(\dfrac{a}{12}\)=\(\dfrac{7}{6}\):\(\dfrac{2}{3}\)=\(\dfrac{21}{12}\)
=>a=21.
VV
3
H9
HT.Phong (9A5)
CTVHS
28 tháng 7 2023
a) \(2+\dfrac{3}{4}\)
\(=\dfrac{8}{4}+\dfrac{3}{4}\)
\(=\dfrac{8+3}{4}\)
\(=\dfrac{11}{4}\)
b) \(\dfrac{1}{3}+\dfrac{3}{2}-\dfrac{7}{4}\)
\(=\dfrac{4}{12}+\dfrac{18}{12}-\dfrac{21}{12}\)
\(=\dfrac{4+18-21}{12}\)
\(=\dfrac{1}{12}\)
c) \(\dfrac{1}{6}+\dfrac{3}{8}-\dfrac{1}{4}\)
\(=\dfrac{4}{24}+\dfrac{9}{24}-\dfrac{6}{24}\)
\(=\dfrac{4+9-6}{24}\)
\(=\dfrac{7}{24}\)
d) \(\dfrac{5}{12}+\dfrac{3}{8}\times\dfrac{4}{9}\)
\(=\dfrac{5}{12}+\dfrac{3\times4}{8\times9}\)
\(=\dfrac{5}{12}+\dfrac{1}{6}\)
\(=\dfrac{5}{12}+\dfrac{2}{12}\)
\(=\dfrac{7}{12}\)
e) \(\dfrac{4}{5}-\dfrac{1}{5}\times\dfrac{7}{2}\)
\(=\dfrac{4}{5}-\dfrac{1\times7}{5\times2}\)
\(=\dfrac{4}{5}-\dfrac{7}{10}\)
\(=\dfrac{8}{10}-\dfrac{7}{10}\)
\(=\dfrac{8-7}{10}\)
\(=\dfrac{1}{10}\)
f) \(\dfrac{16}{9}-\dfrac{4}{15}:\dfrac{2}{5}\)
\(=\dfrac{16}{9}-\dfrac{4}{15}\times\dfrac{5}{2}\)
\(=\dfrac{16}{9}-\dfrac{4\times5}{15\times2}\)
\(=\dfrac{16}{9}-\dfrac{2}{3}\)
\(=\dfrac{16}{9}-\dfrac{6}{9}\)
\(=\dfrac{16-6}{9}\)
\(=\dfrac{10}{9}\)
28 tháng 7 2023
a: =8/4+3/4=11/4
b: =4/12+18/12-21/12=1/12
c: =4/24+9/24-6/24=7/24
d: =5/12+12/72
=5/12+1/6
=5/12+2/12=7/12
e: =4/5-7/10
=8/10-7/10=1/10
f: =16/9-4/15*5/2
=16/9-20/30
=16/9-2/3
=16/9-6/9=10/9
OM
2
13 tháng 1
a) \(2\times\dfrac{2}{3}=\dfrac{2}{1}\times\dfrac{2}{3}=\dfrac{2\times2}{1\times3}=\dfrac{4}{3}\)
b) \(\dfrac{6}{5}+\dfrac{1}{9}=\dfrac{54}{45}+\dfrac{5}{45}=\dfrac{54+5}{45}=\dfrac{59}{45}\)
c) \(\dfrac{12}{7}\div\dfrac{2}{6}=\dfrac{12}{7}\times\dfrac{6}{2}=\dfrac{12\times6}{7\times2}=\dfrac{36}{7}\)
d) \(\dfrac{2}{3}\div\dfrac{5}{4}+\dfrac{4}{7}=\dfrac{2}{3}\times\dfrac{4}{5}+\dfrac{4}{7}=\dfrac{8}{15}+\dfrac{4}{7}=\dfrac{56}{105}+\dfrac{60}{105}=\dfrac{56+60}{105}=\dfrac{116}{105}\)
C
13 tháng 1
\(a.2\times\dfrac{2}{3}=\dfrac{4}{3}\)
\(b.\dfrac{6}{5}+\dfrac{1}{9}=\dfrac{54}{45}+\dfrac{5}{45}=\dfrac{59}{45}\)
\(c.\dfrac{12}{7}:\dfrac{2}{6}=\dfrac{12}{7}\times\dfrac{6}{2}=\dfrac{72}{14}=\dfrac{36}{7}\)
\(d.\dfrac{2}{3}:\dfrac{5}{4}+\dfrac{4}{7}=\dfrac{2}{3}\times\dfrac{4}{5}+\dfrac{4}{7}=\dfrac{8}{15}+\dfrac{4}{7}=\dfrac{56}{105}+\dfrac{60}{105}=\dfrac{116}{105}\)
N
10
31 tháng 8 2017
a)=\(\frac{9}{4}\)
b)=\(\frac{89}{50}\)
c)=\(\frac{7}{9}\)
d)=\(\frac{26}{7}\)
S
3
17 tháng 5 2017
a) \(3\frac{2}{7}=\frac{3.7+2}{7}=\frac{23}{7}\) b) \(2\frac{5}{12}=\frac{2.12+5}{12}=\frac{29}{12}\)
c) \(9\frac{5}{9}=\frac{9.9+5}{9}=\frac{86}{9}\) d) \(12\frac{3}{4}=\frac{12.4+3}{4}=\frac{51}{4}\)
17 tháng 5 2017
a . \(3\frac{2}{7}=\frac{3\cdot7+2}{7}=\frac{23}{7}\)
b . \(2\frac{5}{12}=\frac{2\cdot12+5}{12}\frac{29}{12}\)
c . \(9\frac{5}{9}=\frac{9\cdot9+5}{9}=\frac{86}{9}\)
d . \(12\frac{3}{4}=\frac{12\cdot4+3}{4}=\frac{51}{4}\)
LN
26 tháng 6 2018
a) 1+2+3+...+2018
=[(2018-1):1+1].(2018+1):2
=2018.2019:2
=2037171
b) 4+7+10+13+...+2017
=[(2017-4):3+1].(2017+4):2
=672.2021:2
=679056
c) 1+2-3-4+5+6-7-8+9+10-11-12+13+14
=(1+2-3-4)+(5+6-7-8)+(9+10-11-12)+13+14
=-4+(-4)+(-4)+13+14
=-12+27
=15
d) 23 x 75 + 25 x 23 + 180
=23 x (75+25) +180
=23 x 100 +180
=2300+180
2480
chúc ban hoc tốt nha
26 tháng 6 2018
a) Số số hạng: ( 2018 - 1 ) : 1 + 1 = 2018
Tổng: 2018 x ( 2018 + 1 ) : 2 = 2 037 171
`2/9 xx 7/12 = (2xx7)/(9xx12) = 14/108= 7/54`
`3/11 xx 12/5 = (3xx12)/(11xx5) = 36/55`
`3 xx 7/9 = (3xx7)/9 = 21/9=7/3`
`4/15 xx 6 = (4xx6)/15 = 24/15 = 8/5`