Bài 1
\(\Leftrightarrow\left(x-4\right)\left(x+2\right)=4\sqrt{-\left(x-4\right)\left(x+2\right)}\)
\(\Leftrightarrow\sqrt{-16\left(x-4\right)\left(x+2\right)}=\left(x-4\right)\left(x+2\right)\)
\(\Leftrightarrow-16\left(x-4\right)\left(x+2\right)=\left(x-4\right)^2\cdot\left(x+2\right)^2\)
\(\Leftrightarrow\left(x-4\right)\left(x+2\right)=0\)
=>x=4 hoặc x=-2
=>Số nghiệm là 2 nghiệm