a: \(=\dfrac{1}{2}\cdot\dfrac{3}{4}\cdot\dfrac{5}{6}=\dfrac{15}{48}=\dfrac{5}{16}\)

b: \(=\dfrac{2}{3}+\dfrac{12}{42}=\dfrac{2}{3}+\dfrac{2}{7}=\dfrac{20}{21}\)

c: \(=\dfrac{24}{5}\cdot\dfrac{5}{12}=2\)

d: \(=\dfrac{1}{9}+\dfrac{3}{4}=\dfrac{4+27}{36}=\dfrac{31}{36}\)

\(\dfrac{1}{2}\times\dfrac{3}{4}:\dfrac{6}{5}=\dfrac{3}{8}:\dfrac{6}{5}=\dfrac{5}{16}\)

\(\dfrac{2}{3}+\dfrac{1}{6}:\dfrac{7}{12}=\dfrac{2}{3}+\dfrac{2}{7}=\dfrac{14}{21}+\dfrac{6}{21}=\dfrac{20}{21}\)

\(8\times\dfrac{3}{5}:\dfrac{12}{5}=\dfrac{24}{5}:\dfrac{12}{5}=2\)

\(\dfrac{4}{9}+\dfrac{3}{4}-\dfrac{1}{3}=\dfrac{16}{36}+\dfrac{27}{36}-\dfrac{12}{36}=\dfrac{31}{36}\)

b: \(\left(x^2+10x+8\right)^2-\left(8x+4\right)\left(x^2+8x+7\right)\)

\(=\left\lbrack\left(x^2+8x+7\right)+\left(2x+1\right)\right\rbrack^2-4\left(2x+1\right)\left(x^2+8x+7\right)\)

\(=\left(x^2+8x+7\right)^2+2\left(x^2+8x+7\right)\left(2x+1\right)+\left(2x+1\right)^2-4\left(2x+1\right)\left(x^2+8x+7\right)\)

\(=\left(x^2+8x+7\right)^2-2\left(x^2+8x+7\right)\left(2x+1\right)+\left(2x+1\right)^2\)

\(=\left(x^2+8x+7-2x-1\right)^2=\left(x^2+6x+6\right)^2\)

d: \(B=x^4+4x^3+8x^2+8x+4\)

\(=x^4+2x^3+2x^2+2x^3+4x^2+4x+2x^2+4x+4\)

\(=x^2\left(x^2+2x+2\right)+2x\left(x^2+2x+2\right)+2\left(x^2+2x+2\right)\)

\(=\left(x^2+2x+2\right)\left(x^2+2x+2\right)=\left(x^2+2x+2\right)^2\)

e: \(C=x^4-2x^3+5x^2-4x+4\)

\(=x^4-x^3+2x^2-x^3+x^2-2x+2x^2-2x+4\)

\(=x^2\left(x^2-x+2\right)-x\left(x^2-x+2\right)+2\left(x^2-x+2\right)=\left(x^2-x+2\right)\left(x^2-x+2\right)\)

\(=\left(x^2-x+2\right)^2\)

1: \(=\dfrac{3}{8}\cdot\dfrac{5}{6}=\dfrac{15}{24}=\dfrac{5}{8}\)

2: \(=\dfrac{2}{3}+\dfrac{12}{42}=\dfrac{2}{3}+\dfrac{2}{7}=\dfrac{14+6}{21}=\dfrac{20}{21}\)

3: \(=\dfrac{24}{5}\cdot\dfrac{5}{12}=2\)

4: \(=\dfrac{1}{3}+\dfrac{3}{4}=\dfrac{4+9}{12}=\dfrac{13}{12}\)

`1/2xx3/4:6/5= 1/2 xx 3/4 xx 5/6 = 3/8 xx 5/6 =5/16`           

`2/3+1/6:7/12 = 2/3 + 1/6 xx 12/7 = 2/3 + 2/7 = 14/21 + 6/21 = 20/21`       

`8xx3/5:12/5= 8xx 3/5 xx 5/12 = 24/5 xx 5/12 = 2`         

`4/9+3/4-1/3= (16/36 + 27/36 ) - 1/3 = 43/36 - 1/3 = 31/36`

a, 3x2 - 8x2 - 2x+3=0

2x(3-8) - 2x+3=0

2x5 - 2x+3=0

2x5 - 2x=0-3=

2x5 - 2x=-3

2x(5-x)=-3

5-x=-3/2

5-x=1,5

x=5-1,5

x=3,5

3,5 nha bn

chúc bn học tốt

happy new year

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Bài 1: 

a: \(8x^3-2x=2x\left(4x^2-1\right)=2x\left(2x-1\right)\left(2x+1\right)\)

c: \(-5m^3\left(m+1\right)+m+1=\left(m+1\right)\left(-5m^3+1\right)\)

Bài 1: B

Bài 2: A

1: B

2: A