Ta có:\(\frac{\left[x\left(x-2\right)\right]}{x^2+8x-20}+12x-3=\frac{x\left(x-2\right)}{x^2-2x+10x-20}+12x-3\)
\(=\frac{x\left(x-2\right)}{x\left(x-2\right)+10\left(x-2\right)}+12x-3=\frac{x\left(x-2\right)}{\left(x+10\right)\left(x-2\right)}+12x-3\)
\(=\frac{x}{x+10}+12x-3=\frac{x+\left(12x-3\right).\left(x+10\right)}{x+10}=\frac{x+12x^2+120x-3x-30}{x+10}\)
\(=\frac{12x^2+118x-30}{x+10}\)