Bài 5: Quy đồng mẫu nhiều phân số

Đề thiếu rồi bạn

BCNN(28,42,56,..) nhé

tham khảo :
Tìm BCNN 14 , 21 | Mathway

x=-2/3-7/15=-17/15

\(x+\dfrac{7}{15}=\dfrac{-24}{36}\\ x=\dfrac{-24}{36}-\dfrac{7}{15}\\ x=\dfrac{-2}{3}-\dfrac{7}{15}\\ x=\dfrac{-10}{15}-\dfrac{7}{15}\\ x=\dfrac{-17}{15}\)

\(T=3+3^2+3^3+3^4+3^5+3^6+3^7+3^8+3^9+3^{10}+3^{11}+3^{12}\)

\(=3\left(1+3+3^2+3^3+3^4+3^5+3^6+3^7+3^8+3^9+3^{10}+3^{11}\right)\)⋮3

Vậy ...

Bài 1: 

a: \(\dfrac{475}{450}=\dfrac{19}{18}\)

b: \(\dfrac{14\cdot18}{21\cdot36}=\dfrac{2}{3}\cdot\dfrac{1}{2}=\dfrac{1}{3}\)

c: \(\dfrac{15\cdot13-15\cdot17}{4\cdot7+4\cdot8}=\dfrac{15\cdot\left(-4\right)}{15\cdot4}=-1\)

d: \(\dfrac{3\cdot5\cdot7\cdot11\cdot13\cdot37-10101}{1212120+40404}=\dfrac{27}{62}\)

Làm cho mình bài 6,7 nhé

Bài 6: 

a) \(\dfrac{4}{9}=\dfrac{4}{9}\)

\(\dfrac{5}{3}=\dfrac{5\cdot3}{3\cdot3}=\dfrac{15}{9}\)

b) \(\dfrac{3}{14}=\dfrac{3\cdot3}{14\cdot3}=\dfrac{9}{42}\)

\(\dfrac{5}{6}=\dfrac{5\cdot7}{6\cdot7}=\dfrac{35}{42}\)

c) \(\dfrac{-2}{25}=\dfrac{-2\cdot7}{25\cdot7}=\dfrac{-14}{175}\)

\(\dfrac{3}{-35}=\dfrac{-3}{35}=\dfrac{-3\cdot5}{35\cdot5}=\dfrac{-15}{175}\)

quy đồng mẫu số: 3/70; -5/4; 11/20 

3/70=6/140

-5/4=-175/140

11/20=77/140

\(\dfrac{3}{70(2)};\dfrac{-5}{4(35)};\dfrac{11}{20(7)}\)

BCNN(70;4;20)=\(2^2 . 5.7\) = 140

\(\dfrac{3}{70}=\dfrac{3.2}{70.2}=\dfrac{5}{140};\dfrac{-5}{4}=\dfrac{(-5).35}{4.35}=\dfrac{-175}{140};\dfrac{11}{20}=\dfrac{11.7}{20.7}=\dfrac{77}{140}.\)

-6=-66/11

1/11=1/11

C1: Quy đồng mẫu số

C2: Quy đồng tử số

C1: Quy đồng mẫu số

C2: Quy đồng tử số

C1: Quy đồng mẫu số

C2: Quy đồng tử số