Bn tìm ra Mẫu số Chung là sẽ bt đc

Cách đơn giản là bn bấm máy tính

=)))

a) Ta có: 15 = 3 . 5; 45 = 3^2 . 5; 4 = 2^2

=> MC = 2^2 . 3^2 . 5 = 4 . 9 . 5 = 36 . 5 = 180

14/15 = 14 . 12/ 15 . 12 = 168/180

47/45 = 47 . 4/ 45 . 4 = 188/180

5/4 = 5 . 45/4 . 45 = 225/180

Vậy quy đồng mẫu số các phân số 14/15; 47/45 và 5/4 ta được 168/180; 188/180 và 225/180

b) Ta có: 12 = 2^2 . 3; 18 = 2 . 3^2; 24 = 2^3 . 3

=> MC = 2^3 . 3^2 = 8 . 9 = 72

7/12 = 7 . 6/12 . 6 = 42/72

11/18 = 11 . 4/18 . 4 = 44/72

25/24 = 25 . 3/24 . 3 = 75/72

Vậy quy đồng mẫu số các phân số 7/12; 11/18 và 25/24 ta được 42/72; 44/72 và 75/72

a) -1/3

b)8/3

c)2

k cho mk nha mk cảm ơn nhiều

\(a.\frac{27.45+27.55}{2+4+6+...+14+16+18}=\frac{27.100}{\frac{\left(2+18\right).9}{2}}=30\)

\(b.\frac{26.108-26.12}{32-28+24-20+16-12+8-4}=\frac{26\left(108-12\right)}{\left(32-28\right).4}=\frac{26.96}{4.4}=156\)

\(c.\frac{27.4500+135.550.2}{2+4+6+...+14+16+18}=\frac{270.450+270.550}{\frac{\left(2+8\right).9}{2}}\)

\(d.\frac{48.700-24.45.20}{45-40+35-30+25-20+15-10+5}=\frac{48.700-48.450}{5.5}\)\(=\frac{48\left(700-450\right)}{25}=\frac{48.250}{25}=480\)

#ĐinhBa

\(\frac{9}{27}+\frac{8}{24}+\frac{18}{27}+\frac{16}{24}+\frac{2}{3}\)

=\(\frac{1}{3}+\frac{1}{3}+\frac{2}{3}+\frac{2}{3}+\frac{2}{3}\)

\(=\frac{8}{3}\)

\(\frac{9}{27}+\frac{8}{24}+\frac{18}{27}-\frac{-16}{24}+\frac{2}{3}\)

\(=\frac{9}{27}+\frac{8}{24}+\frac{18}{27}+\frac{16}{24}+\frac{2}{3}\)

\(=\frac{1}{3}+\frac{1}{3}+\frac{2}{3}+\frac{2}{3}+\frac{2}{3}\)

\(=\left[\frac{1}{3}+\frac{2}{3}\right]+\left[\frac{1}{3}+\frac{2}{3}\right]+\frac{2}{3}\)

\(=1+1+\frac{2}{3}=2+\frac{2}{3}=\frac{8}{3}\)

\(\frac{9}{27}+\frac{8}{24}+\frac{18}{27}-\frac{-16}{24}+\frac{2}{3}\)

\(\frac{1}{3}+\frac{1}{3}+\frac{2}{3}+\frac{2}{3}+\frac{2}{3}\)

\(\frac{2}{3}+\frac{2}{3}+\frac{2}{3}+\frac{2}{3}\)

\(\frac{8}{3}\)

Đặt \(A=\frac{9+\frac{9}{11}+\frac{18}{23}-\frac{27}{37}}{8+\frac{8}{11}+\frac{16}{23}-\frac{24}{37}}-\frac{2+\frac{16}{29}-\frac{24}{13}-\frac{32}{11}}{3+\frac{24}{29}-\frac{36}{13}-\frac{48}{11}}\)\(=\frac{9\left(1+\frac{1}{11}+\frac{2}{23}-\frac{3}{37}\right)}{8\left(1+\frac{1}{11}+\frac{2}{23}-\frac{3}{37}\right)}-\frac{2\left(1+\frac{8}{29}-\frac{12}{13}-\frac{16}{11}\right)}{3\left(1+\frac{8}{29}-\frac{12}{13}-\frac{16}{11}\right)}\)

\(=\frac{9}{8}-\frac{2}{3}\)(do \(1+\frac{1}{11}+\frac{2}{23}-\frac{3}{37};1+\frac{8}{29}-\frac{12}{13}-\frac{16}{11}\ne0\))

\(=\frac{27}{24}-\frac{16}{24}=\frac{11}{24}.\)

Vậy A = \(\frac{11}{24}.\)

\(\frac{18}{24}=\frac{18:6}{24:6}=\frac{3}{4}\)

\(\frac{15}{25}=\frac{15:5}{25:5}=\frac{3}{5}\)

\(\frac{3}{4}>\frac{3}{5}\)   vì cùng bằng tử số, mẫu số của phân số nào lớn thì nhỏ hơn

2) a)   \(\frac{24}{32}=\frac{3}{4}\) 

\(\frac{9}{21}=\frac{3}{7}\)        \(\Rightarrow\frac{3}{4}>\frac{3}{7}\)   ( giải thích tương tự như trên)

những câu sau tương tự 

Bài 1

\(\frac{18}{24}=\frac{18:6}{24:6}=\frac{3}{4}\)

\(\frac{15}{25}=\frac{15:5}{25:5}=\frac{3}{5}\)

Vì 4 < 5 => \(\frac{3}{4}>\frac{3}{5}\)( Cùng tử, mẫu số nào nhỏ hơn thì p.s đó lớn hơn )

=> \(\frac{18}{24}>\frac{15}{25}\)

Bài 2. 

a) \(\frac{24}{32}\)và \(\frac{9}{21}\)

\(\frac{24}{32}=\frac{24:8}{32:8}=\frac{3}{4}\); \(\frac{9}{21}=\frac{9:3}{21:3}=\frac{3}{7}\)

Vì 4 < 7 => \(\frac{3}{4}>\frac{3}{7}\)=> \(\frac{24}{32}>\frac{9}{21}\)

\(\frac{15}{25}\)và \(\frac{12}{15}\)

\(\frac{15}{25}=\frac{15:5}{25:5}=\frac{3}{5}\); \(\frac{12}{15}=\frac{12:3}{15:3}=\frac{4}{5}\)

Vì 3 < 4 => \(\frac{3}{5}< \frac{4}{5}\)=> \(\frac{15}{25}< \frac{12}{15}\)

b) \(\frac{5}{6}\)và \(\frac{6}{5}\)

Ta có : \(\frac{5}{6}< 1< \frac{6}{5}\)

=> \(\frac{5}{6}< \frac{6}{5}\)

\(\frac{7}{5}\)và \(\frac{5}{3}\)

Quy đồng mẫu số ta được : \(\frac{7}{5}=\frac{7\cdot3}{5\cdot3}=\frac{21}{15}\); \(\frac{5}{3}=\frac{5\cdot5}{3\cdot5}=\frac{25}{15}\)

Vì 21 < 25 => \(\frac{21}{15}< \frac{25}{15}\)=> \(\frac{7}{5}< \frac{5}{3}\)

a) \(\frac{-6}{35}.\frac{-49}{60}=\frac{\left(-6\right).\left(-49\right)}{35.60}=\frac{\left(-6\right).\left(-7\right).\left(-7\right)}{\left(-5\right).\left(-7\right).\left(-6\right).\left(-10\right)}=\frac{-7}{\left(-5\right).\left(-10\right)}=\frac{-7}{50}\)

b) \(\frac{-16}{25}.\frac{-5}{24}=\frac{\left(-16\right).\left(-5\right)}{25.24}=\frac{\left(-8\right).2.\left(-5\right)}{\left(-5\right).\left(-5\right).\left(-8\right).\left(-3\right)}=\frac{2}{\left(-5\right).\left(-3\right)}=\frac{2}{15}\)

c) \(\frac{15}{-17}.\frac{5}{18}=\frac{15.5}{\left(-17\right).18}=\frac{5.3.5}{\left(-17\right).3.6}=\frac{5.5}{\left(-17\right).6}=\frac{25}{-102}\)

a) \(\frac{-6}{35}\cdot\frac{-49}{60}\)

\(=\frac{\left(-6\right)\cdot\left(-49\right)}{35\cdot60}\)

\(=\frac{294}{2100}=\frac{7}{50}\)

b)\(\frac{-16}{25}\cdot\frac{-5}{24}\)

\(=\frac{\left(-16\right)\cdot\left(-5\right)}{25\cdot24}\)

\(=\frac{80}{600}=\frac{2}{15}\)

c)\(\frac{15}{-17}\cdot\frac{5}{18}\)

\(=\frac{15\cdot5}{\left(-17\right)\cdot18}\)

\(=\frac{75}{-306}=\frac{25}{-102}\)

a, = 7/50

b, = 2/15

c, = -25/102

Tk mk nha