a) \(x^2\left(x+2\right)-2x\left(x+1\right)-\left(x^3-x+4\right)=0\)
\(\Leftrightarrow x^3+2x^2-2x^2-2x-x^3+x-4=0\)
\(\Leftrightarrow-\left(x+4\right)=0\Leftrightarrow x=-4\)
b) \(\left(2x+1\right)^2-\left(2x-3\right).\left(2x+3\right)=3.\left(x+2\right)\)
\(\Rightarrow\left(2x+1\right)^2-\left(2x-3\right).\left(2x+3\right)-3.\left(x+2\right)=0\)
\(\Rightarrow\left(2x\right)^2+2.2x.1+1-\left[\left(2x\right)^2-3^2\right]-\left(3x+6\right)=0\)
\(\Rightarrow4x^2+4x+1-\left(4x^2-9\right)-\left(3x+6\right)=0\)
\(\Rightarrow4x^2+4x+1-4x^2+9-3x-6=0\)
\(\Rightarrow1x+4=0\)
\(\Rightarrow1x=0-4\)
\(\Rightarrow1x=-4\)
\(\Rightarrow x=-4\)
Vậy \(x=-4.\)
Chúc bạn học tốt!
