A

D

6.D

7.D

6.D

7.C

8. B

9.A

\(\left(x-5\right)\left(x-1\right)=\left(2x+1\right)\left(\dfrac{1}{2}x-3\right)\\ \Leftrightarrow x^2-6x+5=x^2-\dfrac{11}{2}x-3\\ \Leftrightarrow x^2-6x+5-x^2+\dfrac{11}{2}x+3=0\\ \Leftrightarrow-\dfrac{1}{2}x+8=0\\ \Leftrightarrow x=16\)

\(\left(2x-1\right)\left(x-3\right)=-2x+2\\ \Leftrightarrow2x^2-x-6x+3+2x-2=0\\ \Leftrightarrow2x^2-5x+1=0\)

\(\Delta=\left(-5\right)^2-4.2.1=25-8=17>0\)

\(x_1=\dfrac{-\left(-5\right)+\sqrt{17}}{2.2}=\dfrac{5+\sqrt{17}}{4}\)

\(x_1=\dfrac{-\left(-5\right)-\sqrt{17}}{2.2}=\dfrac{5-\sqrt{17}}{4}\)

bài 6 sai r

Bài 6:
\(\dfrac{5}{8}:x=2-\dfrac{3}{14}\\ \Rightarrow\dfrac{5}{8}:x=\dfrac{28}{14}-\dfrac{3}{14}\\ \Rightarrow\dfrac{5}{8}:x=\dfrac{25}{14}\\ \Rightarrow x=\dfrac{5}{8}:\dfrac{25}{14}\\ \Rightarrow x=\dfrac{7}{20}\)

Bài 7:

\(\dfrac{3}{7}\times\dfrac{8}{13}+\dfrac{3}{7}\times\dfrac{5}{13}\\ =\dfrac{3}{7}\times\left(\dfrac{8}{13}+\dfrac{5}{13}\right)\\ =\dfrac{3}{7}\times\dfrac{13}{13}\\ =\dfrac{3}{7}\times1\\ =\dfrac{3}{7}\)