\(x^2-4-\left(x+5\right)\left(2-x\right)=0\)
\(2x^2-14+3x=0\)
\(2x^2+3x-14=0\)
\(\Delta=b^2-4ac=3^2-4.2.\left(-14\right)=9+112=121>0\)
Nên pt có 2 nghiệm phân biệt
\(x_1=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-3-\sqrt{121}}{2.2}=\frac{-3-11}{4}=-\frac{7}{2}\)
\(x_2=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-3+\sqrt{121}}{2.2}=\frac{-3+11}{4}=\frac{8}{4}=2\)
\(x^2-4-\left(x+5\right)\left(2-x\right)=0\)
\(\Leftrightarrow\left(x-2\right)\left(x+2\right)-\left(x+5\right)\left(2-x\right)=0\)
\(\Leftrightarrow\left(x-2\right)\left(x+2\right)+\left(5-x\right)\left(x-2\right)=0\)
\(\Leftrightarrow\left(x-2\right)\left(x+2+5-x\right)=0\)
\(\Leftrightarrow\left(x-2\right).7=0\)
\(\Leftrightarrow7x-14=0\)
\(\Leftrightarrow7x=14\)
\(\Leftrightarrow x=2\)
