24B

25A

26B

27B vs C đều đúng

28C

29D

30D

b/

\(\dfrac{x-3}{5}-\dfrac{x}{2}=\dfrac{3-x}{10}\)

\(\dfrac{x-3}{5}-\dfrac{x}{2}-\dfrac{3-x}{10}=0\)

\(\dfrac{-2x-9}{10}=0\)

\(-2x-9=0\)

\(\Rightarrow x=\dfrac{0+9}{-2}=\dfrac{-9}{2}\)

2/

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

3/

\(9x^2-\left(x-1\right)^2=\left(3x\right)^2-\left(x-1\right)^2=\left(3x-x+1\right)\left(3x+x-1\right)\)

4/

\(x^2-3x+6y-4y^2=x^2-4y^2-3x+6y=\left(x^2-4y^2\right)-\left(3x-6y\right)\)

\(=\left(x-2y\right)\left(x+2y\right)-3\left(x-2y\right)=\left(x-2y\right)\left(x+2y-3\right)\)

Rút gọn:

\(=\dfrac{1}{x^2+x+1}+\dfrac{1}{x\left(x-1\right)}-\dfrac{2x}{x^3-1}\)

\(=\dfrac{1}{x^2+x+1}+\dfrac{1}{x\left(x-1\right)}-\dfrac{2x}{\left(x-1\right)\left(x^2+x+1\right)}\)

\(=\dfrac{x^2-x}{x\left(x-1\right)\left(x^2+x+1\right)}+\dfrac{x^2+x+1}{x\left(x-1\right)\left(x^2+x+1\right)}-\dfrac{2x^2}{x\left(x-1\right)\left(x^2+x+1\right)}\)

\(=\dfrac{x^2-x+x^2+x+1-2x^2}{x\left(x-1\right)\left(x^2+x+1\right)}\)\(=\dfrac{1}{x\left(x-1\right)\left(x^2+x+1\right)}\)\(=\dfrac{1}{x^4-x}\)

thay x =2 vào bt P, ta có:

\(\dfrac{1}{2^4-2}\)\(=\dfrac{1}{14}\)

cảm ơn lmj chi=lấy thưn béo đép><

Tới công chz quên H2😂

A nha

( có 17 ch chứ nhiiu:))