\(f\left(x\right)+g\left(x\right)=6x^4-3x^2-5\\ f\left(x\right)-g\left(x\right)=4x^4-6x^3+7x^2+8x-9\\ \Rightarrow2f\left(x\right)=6x^4-3x^2-5+4x^4-6x^3+7x^2+8x-9\\ 2f\left(x\right)=10x^4-6x^3+4x^2+8x-14\\ 2f\left(x\right)=2\left(5x^4-3x^3+2x^2+4x-7\right)\\ \Rightarrow f\left(x\right)=5x^4-3x^3+2x^2+8x-14\)

\(f\left(x\right)+g\left(x\right)=6x^4-3x^2-5\\ \Rightarrow g\left(x\right)=6x^4-3x^2-5-f\left(x\right)\\ g\left(x\right)=6x^4-3x^2-5-5x^4+3x^3-2x^2-8x+14\\ g\left(x\right)=x^4+3x^3-5x^2-8x+9\)

b: Đặt \(x^2+5x+4=a\)

\(\Leftrightarrow a=5\sqrt{a+24}\)

\(\Leftrightarrow a^2=25a+600\)

\(\Leftrightarrow a^2-25a-600=0\)

\(\Leftrightarrow\left(a-40\right)\left(a+15\right)=0\)

\(\Leftrightarrow a=-15\)

hay S=∅

$P=\dfrac{2}{x+3}+\dfrac{1}{x-3}+\dfrac{9-x}{9-x^2}$

$=\dfrac{2(x-3)+(x+3)}{(x+3)(x-3)}+\dfrac{9-x}{(3-x)(3+x)}$

$=\dfrac{3x-3}{x^2-9}+\dfrac{9-x}{9-x^2}$

$=\dfrac{3x-3}{x^2-9}-\dfrac{9-x}{x^2-9}$

$=\dfrac{3x-3-9+x}{x^2-9}$

$=\dfrac{4x-12}{x^2-9}$

$=\dfrac{4(x-3)}{(x-3)(x+3)}$

$=\dfrac{4}{x+3}$

Vậy $P=\dfrac{4}{x+3}$.

$(2x^4-3x^3-3x^2+6x-1):(x^2-2)$

$=2x^2-3x+1+\dfrac{4x+1}{x^2-2}$

Vậy thương là $2x^2-3x+1$, dư $4x+1$.

$(15x^4y^6-12x^3y^4-18x^2y^3):(-6x^2y^2)$

$=\dfrac{15x^4y^6}{-6x^2y^2}+\dfrac{-12x^3y^4}{-6x^2y^2}+\dfrac{-18x^2y^3}{-6x^2y^2}$

$=-\dfrac52x^2y^4+2xy^2+3y$

Vậy kết quả là $-\dfrac52x^2y^4+2xy^2+3y$.

\(\frac{x^2+3x+9}{2x+10}.\frac{x+5}{x^3-27}\)

\(=\frac{x^2+3x+9}{2\left(x+5\right)}.\frac{x+5}{\left(x-3\right)\left(x^2+3x+9\right)}\)

\(=\frac{\left(x+5\right)\left(x^2+3x+9\right)}{2\left(x+5\right)\left(x-3\right)\left(x^2+3x+9\right)}\)

\(=\frac{1}{2\left(x-3\right)}\)

\(\left(\frac{6x+1}{x^2-6x}+\frac{6x-1}{x^2+6x}\right)\left(\frac{x^2-36}{x^2+1}\right)\)

\(=\left[\frac{6x+1}{x\left(x-6\right)}+\frac{6x-1}{x\left(x+6\right)}\right]\left[\frac{\left(x-6\right)\left(x+6\right)}{x^2+1}\right]\)

\(=\frac{\left(6x+1\right)\left(x+6\right)+\left(6x-1\right)\left(x-6\right)}{x\left(x-6\right)\left(x+6\right)}.\frac{\left(x-6\right)\left(x+6\right)}{x^2+1}\)

\(=\frac{6x^2+36x+x+6+6x^2-36x-x+6}{x\left(x-6\right)\left(x+6\right)}.\frac{\left(x-6\right)\left(x+6\right)}{x^2+1}\)

\(=\frac{12x^2+12}{x\left(x-6\right)\left(x+6\right)}.\frac{\left(x-6\right)\left(x+6\right)}{x^2+1}\)

\(=\frac{12\left(x^2+1\right).\left(x-6\right)\left(x+6\right)}{x\left(x-6\right)\left(x+6\right)\left(x^2+1\right)}\)

\(=\frac{12}{x}\)

em chưa cho đa thức f(x) và g(x) nà

e cho r