Quy đồng mẫu hai phân số ta có :

\(\frac{4}{7}=\frac{4\times12}{7\times12}=\frac{48}{84}\)

\(\frac{5}{12}=\frac{5\times7}{12\times7}=\frac{35}{84}\)

Ta có : MSC : 396

\(\frac{3}{44}=\frac{3\cdot9}{44\cdot9}=\frac{27}{396}\)

\(\frac{-11}{18}=\frac{-11\cdot22}{18\cdot22}=\frac{-242}{396}\)

\(\frac{5}{-36}=\frac{-5}{36}=\frac{-5\cdot11}{36\cdot11}=\frac{-55}{396}\)

Giải:

\(\dfrac{3}{2}+\dfrac{6}{8}+\dfrac{9}{28}+\dfrac{12}{77}+\dfrac{15}{176}\) 

\(=\dfrac{3}{1.2}+\dfrac{6}{2.4}+\dfrac{9}{4.7}+\dfrac{12}{7.11}+\dfrac{15}{11.16}\) 

\(=3.\left(\dfrac{1}{1.2}+\dfrac{2}{2.4}+\dfrac{3}{4.7}+\dfrac{4}{7.11}+\dfrac{5}{11.16}\right)\) 

\(=3.\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{16}\right)\) 

\(=3.\left(1-\dfrac{1}{16}\right)\) 

\(=3.\dfrac{15}{16}\) 

\(=\dfrac{45}{16}\)

Đặt A = \(\dfrac{3}{2}+\dfrac{6}{8}+\dfrac{9}{28}+\dfrac{12}{77}+\dfrac{15}{176}\)

= \(3\left(\dfrac{1}{1\times2}+\dfrac{2}{2\times4}+\dfrac{3}{4\times7}+\dfrac{4}{7\times11}+\dfrac{5}{11\times16}\right)\)

= \(3\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{16}\right)\)

= \(3\left(1-\dfrac{1}{16}\right)=3\times\dfrac{15}{16}=\dfrac{45}{16}\)

A)\(\frac{3}{5}=\frac{42}{70};\frac{4}{7}=\frac{40}{70};\frac{5}{10}=\frac{35}{70}\)

B)\(\frac{4}{9}=\frac{8}{18};\frac{11}{18}=\frac{11}{18};\frac{5}{6}=\frac{15}{18}\)

1

4/25+3/5=19/25=0.76

7/25-1/5=2/25=0.08

3/5=15/25

=4+15/25

=19/25

cau b lam tuong tu

Quy đồng mẫu số 

3/4 ; 5/7 và 8/3

 3/4 =3x7x3/4x7x3=63/84

5/7=5x4x3/7x4x3=60/84

8/3=8x4x7/3x4x7=224/84

Vậy quy đồng mẫu số ba phân số 3/4 ; 5/7 và 8/3 ta được :63/84 ; 60/84 ; 224/84.

3/4=63/84

5/7=60/84

8/3=224/84

\(\frac{3}{4}=\frac{63}{84}\)

\(\frac{5}{7}=\frac{60}{84}\)

\(\frac{8}{3}=\frac{224}{84}\)

Vậy , quy đồng 3 phân số  \(\frac{3}{4},\frac{5}{7},\frac{8}{3}\) ta được các phân số lần lượt là : \(\frac{63}{84},\frac{60}{84},\frac{224}{84}\)

Hok_Tốt

#Thiên_Hy

a)\(\frac{5}{6}\)và\(\frac{1}{4}\)             b)\(\frac{3}{5}\)và\(\frac{3}{7}\)

c)\(\frac{9}{8}\)và\(\frac{8}{9}\)

mik bt

bít . bạn lên google tìm đuy . mềnh hẳm cóa rảnh :))))))))))