Question

bài 1 tìm x biết

i, x^3+5x^2-4x-20=o

Answer 1

\(\Leftrightarrow x^2\left(x+5\right)-4\left(x+5\right)=0\)

\(\Leftrightarrow\left(x^2-4\right)\left(x+5\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=\pm2\\x=-5\end{cases}}\)

Answer 2

\(x^3+5x^2-4x-20=0\)

\(\Leftrightarrow x^2\left(x+5\right)-4\left(x+5\right)=0\)

\(\Leftrightarrow\left(x^2-4\right)\left(x+5\right)=0\)

\(\Leftrightarrow\left(x+2\right)\left(x-2\right)\left(x+5\right)=0\)

\(\Leftrightarrow\)\(x+2=0\)hoặc \(x-2=0\)hoặc \(x+5=0\)

Vậy tập nghiệm là \(S=\left\{\pm2;5\right\}\)