Bài 1:

a, \(\left(5x^3-4x\right):\left(-2x\right)\)

\(=5x^3:\left(-2x\right)+\left(-4x\right):\left(-2x\right)\)

\(=\dfrac{-5}{2}x^2+2\)

b, \(\left(-2x^5-4x^3+3x^2\right):2x^2\)

\(=-2x^5:2x^2+\left(-4x^3\right):2x^2+3x^2:2x^2\)

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

c, \(\left(-5x^3+15x^2+18x\right):\left(-5x\right)\)

\(=-5x^3:\left(-5x\right)+15x^2:\left(-5x\right)+18x:\left(-5x\right)\)

\(=-x^2-3x-\dfrac{18}{5}\)

d, \(\left(-15x^6-24x^3\right):\left(-3x^2\right)\)

\(=-15x^6:\left(-3x^2\right)+\left(-24x^3\right):\left(-3x^2\right)\)

\(=5x^4+8x\)

Bài 2:

a, \(\left(x^2-2x+1\right):\left(x-1\right)\)

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

\(=\left[x\left(x-1\right)-\left(x-1\right)\right]:\left(x-1\right)\)

\(=\left(x-1\right)^2:\left(x-1\right)=x-1\)

b, \(\left(6x^3-2x^2-9x+3\right):\left(3x-1\right)\)

\(=\left[2x^2\left(3x-1\right)-3\left(3x-1\right)\right]:\left(3x-1\right)\)

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

c, \(\left(x^3-4x^2-x+12\right):\left(x-3\right)\) (sửa đề)

\(=\left(x^3-3x^2-x^2+3x-4x+12\right):\left(x-3\right)\)

\(=\left[x^2\left(x-3\right)-x\left(x-3\right)-4\left(x-3\right)\right]:\left(x-3\right)\)

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

d, \(\left(4x^4+14x^3+21x-9\right):\left(2x^2-3\right)\)

\(=\left(4x^4-6x^2+14x^3-21x+6x^2-9+42x\right):\left(2x^2-3\right)\)

\(=\left[2x^2\left(2x^2-3\right)+7x\left(2x^2-3\right)+3\left(2x^2-3\right)+42x\right]:\left(2x^2-3\right)\)

\(=\left[\left(2x^2-3\right)\left(2x^2+7x+3\right)+42x\right]:\left(2x^2-3\right)\)

\(=2x^2+7x+3+42:\left(2x^2-3\right)\)

$\text{#}Toru$

\(\dfrac{x+1}{99}+\dfrac{x+4}{96}+\dfrac{x+7}{93}+\dfrac{x+9}{91}+4=0\) (sửa đề)

\(\Leftrightarrow\left(\dfrac{x+1}{99}+1\right)+\left(\dfrac{x+4}{96}+1\right)+\left(\dfrac{x+7}{93}+1\right)+\left(\dfrac{x+9}{91}+1\right)=0\)

\(\Leftrightarrow\dfrac{x+100}{99}+\dfrac{x+100}{96}+\dfrac{x+100}{93}+\dfrac{x+100}{91}=0\)

\(\Leftrightarrow\left(x+100\right)\left(\dfrac{1}{99}+\dfrac{1}{96}+\dfrac{1}{93}+\dfrac{1}{91}\right)=0\)

\(\Leftrightarrow x+100=0\) (vì \(\dfrac{1}{99}+\dfrac{1}{96}+\dfrac{1}{93}+\dfrac{1}{91}>0\))

\(\Leftrightarrow x=-100\)

Tỉ số của hai số đó là:

2/3 : 1/4 = 8/3