Question

[Thu Trang Nguyễn]

Tìm x :

A) 3.(5/3x-7)-2.(1,5x+6)-(5-x).(x+4)=80+x²

^{B) 4/5x^2 .(2/3-1/2).(1/5x-2/3).(4x^2/3 + 1)=22/45x^2}

Answer 1

[Nguyễn Lê Phước Thịnh]

a: =>5x-21-3x-12+(x-5)(x+4)=80+x²

\(\Leftrightarrow x^2-x-20+2x-33=x^2+80\)

=>x-53=80

hay x=133

b: \(\Leftrightarrow\left(\dfrac{1}{5}x-\dfrac{2}{3}\right)\cdot\left(\dfrac{4}{3}x^2+1\right)\cdot\dfrac{1}{6}=\dfrac{22}{45}:\dfrac{4}{5}=\dfrac{11}{18}\)

\(\Leftrightarrow\left(\dfrac{1}{5}x-\dfrac{2}{3}\right)\left(\dfrac{4}{3}x^2+1\right)=\dfrac{11}{3}\)

\(\Leftrightarrow\dfrac{4}{15}x^3+\dfrac{1}{5}x-\dfrac{8}{9}x^2-\dfrac{2}{3}-\dfrac{11}{3}=0\)

\(\Leftrightarrow\dfrac{4}{15}x^3-\dfrac{8}{9}x^2+\dfrac{1}{5}x-\dfrac{13}{3}=0\)

\(\Leftrightarrow12x^3-40x^2+9x-195=0\)

hay \(x\in\left\{\dfrac{10+\sqrt{685}}{6};\dfrac{10-\sqrt{685}}{6}\right\}\)