\(B=\dfrac{x^2+39}{\left(x-3\right)\left(x+3\right)}+\dfrac{8}{x+3}-\dfrac{1}{x-3}\)
\(=\dfrac{x^2+39+8x-24-x-3}{\left(x-3\right)\left(x+3\right)}=\dfrac{x^2+7x+12}{\left(x-3\right)\left(x+3\right)}\)
\(=\dfrac{\left(x+3\right)\left(x+4\right)}{\left(x-3\right)\left(x+3\right)}=\dfrac{x+4}{x-3}\)
\(B=\dfrac{x^2+39}{x^2-9}+\dfrac{8}{x+3}+\dfrac{1}{3-x}\) (ĐK: \(x\ne3,x\ne-3\))
\(B=\dfrac{x^2+39}{\left(x+3\right)\left(x-3\right)}+\dfrac{8\left(x-3\right)}{\left(x+3\right)\left(x-3\right)}-\dfrac{1}{x-3}\)
\(B=\dfrac{x^2+39+8x-24}{\left(x+3\right)\left(x-3\right)}-\dfrac{1}{x-3}\)
\(B=\dfrac{x^2+8x+15}{\left(x+3\right)\left(x-3\right)}-\dfrac{x+3}{\left(x+3\right)\left(x-3\right)}\)
\(B=\dfrac{x^2+8x+15-x-3}{\left(x+3\right)\left(x-3\right)}\)
\(B=\dfrac{x^2+7x+12}{\left(x+3\right)\left(x-3\right)}\)
\(B=\dfrac{\left(x+3\right)\left(x+4\right)}{\left(x-3\right)\left(x+3\right)}\)
\(B=\dfrac{x+4}{x-3}\)
