Bai 1
\(x^2+x-30=x^2+6x-5x-30=\left(x-5\right)\left(x+6\right)\)
Bai 2
a, \(\left(x-2\right)^2-x\left(x-5\right)=13\)
\(\Leftrightarrow x^2-4x+4-x^2+5x=13\)
\(\Leftrightarrow x+4=13\Leftrightarrow x=9\)
b, \(4x^3-100x=0\Leftrightarrow x\left(4x^2-100\right)=0\)
\(\Leftrightarrow x\left(2x-10\right)\left(2x+10\right)=0\Leftrightarrow x=0;\pm5\)