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28 tháng 6 2016
3/5 × 11/19 + 3/5 × 8/19 + 2/5
= 3/5 × (11/19 + 8/19) + 2/5
= 3/5 × 1 + 2/5
= 3/5 + 2/5
= 1
Ủng hộ mk nha ♡_♡
NT
0
25 tháng 8 2021
Ta có: \(M\cdot N\)
\(=\dfrac{1}{3}\cdot\dfrac{5}{7}\cdot\dfrac{7}{9}\cdot\dfrac{13}{15}\cdot...\cdot\dfrac{37}{39}\cdot\dfrac{7}{5}\cdot\dfrac{11}{9}\cdot...\cdot\dfrac{39}{37}\)
\(=\dfrac{1}{3}\)
XG
1
7 tháng 9 2021
Ta có: M⋅N
=1/3⋅5/7⋅7/9⋅13/15⋅...⋅37/39⋅7/5⋅11/9⋅...⋅39/37
=1/3
NV
1
VA
21 tháng 7 2016
\(\frac{2}{1.3}+\frac{3}{3.6}+\frac{4}{6.10}+\frac{5}{10.15}+\frac{6}{15.21}\)
= \(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{6}+\frac{1}{6}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+\frac{1}{15}-\frac{1}{21}\)
= \(1-\frac{1}{21}\)
= \(\frac{20}{21}\)
Ủng hộ mk nha !!! ^_^
20 tháng 6 2021
Giải:
\(B=\dfrac{3}{3\times5}+\dfrac{3}{5\times7}+\dfrac{3}{7\times9}+...+\dfrac{3}{48\times50}\)
\(B=\dfrac{3}{2}\times\left(\dfrac{2}{3\times5}+\dfrac{2}{5\times7}+\dfrac{2}{7\times9}+...+\dfrac{2}{48\times50}\right)\)
\(B=\dfrac{3}{2}\times\left(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{48}-\dfrac{1}{50}\right)\)
\(B=\dfrac{3}{2}\times\left(\dfrac{1}{3}-\dfrac{1}{50}\right)\)
\(B=\dfrac{3}{2}\times\dfrac{47}{150}\)
\(B=\dfrac{47}{100}\)
Chúc em học tốt!
TV
2
16 tháng 4 2017
a) 3/2:9/4+21/8
= 3/2 x 4/9 + 21/8
=12/18 + 21/8
= 2/3 + 21/8 = 16/24 + 63/24 = 79/24
b) 3/10+5/2x1/3
=3/10 + 5/6
= 9/30 + 25/30 = 34/30 = 17/15
c) 8/15:3/11+2/15:2/11
= 8/15x11/3 + 2/15x11/2
= 88/45 + 22/30
= 88/45 + 11/15 = 88/45 + 33/45 = 121/45
d) 19/5-11/4:9/8
= 19/5 - 11/4x8/9
= 19/5 - 88/36
= 19/5 - 22/9 = 171/45 - 110/45 = 61/45
e) 33/7:11/6+37/15x21/74
= 33/7x6/11 + 7/10
= 198/77 + 7/10 = 1980/770 + 1386/770 = 153/35
4 tháng 9 2022
a) 3/2:9/4+21/8
= 3/2 x 4/9 + 21/8
=12/18 + 21/8
= 2/3 + 21/8 = 16/24 + 63/24 = 79/24
b) 3/10+5/2x1/3
=3/10 + 5/6
= 9/30 + 25/30 = 34/30 = 17/15
c) 8/15:3/11+2/15:2/11
= 8/15x11/3 + 2/15x11/2
= 88/45 + 22/30
= 88/45 + 11/15 = 88/45 + 33/45 = 121/45
d) 19/5-11/4:9/8
= 19/5 - 11/4x8/9
= 19/5 - 88/36
= 19/5 - 22/9 = 171/45 - 110/45 = 61/45
e) 33/7:11/6+37/15x21/74
= 33/7x6/11 + 7/10
= 198/77 + 7/10 = 1980/770 + 1386/770 = 153/35
\(A=\frac{1}{3\times5}+\frac{3}{5\times11}+\frac{2}{11\times15}+\frac{3}{15\times21}\)
\(A=\frac{1}{2}\times\left(\frac{2}{3\times5}+\frac{6}{5\times11}+\frac{4}{11\times15}+\frac{6}{15\times21}\right)\)
\(A=\frac{1}{2}\times\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{11}+\frac{1}{11}-\frac{1}{15}+\frac{1}{15}-\frac{1}{21}\right)\)
\(A=\frac{1}{2}\times\left(\frac{1}{3}-\frac{1}{21}\right)\)
\(A=\frac{1}{2}\times\frac{2}{7}\)
\(A=\frac{1}{7}\)
A = \(\frac{1}{3.5}+\frac{3}{5.11}+\frac{2}{11.15}+\frac{3}{15.21}\)
A = \(\frac{1}{2}.\left(\frac{2}{3.5}+\frac{6}{5.11}+\frac{4}{11.15}+\frac{6}{15.21}\right)\)
A = \(\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{11}+\frac{1}{11}-\frac{1}{15}+\frac{1}{15}-\frac{1}{21}\right)\)
A = \(\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{21}\right)\)
A = \(\frac{1}{2}.\frac{2}{7}\)
A = \(\frac{1}{7}\)