Lời giải:
a. $(x-5)(x+5)+(5-2x)^2=(x^2-5^2)+(25-20x+4x^2)$
$=x^2-25+4x^2-20x+25$
$=5x^2-20x$
b.
$=\frac{-2x}{x(x+1)}+\frac{3(x+1)}{x(x+1)}-\frac{3x}{x(x+1)}$
$=\frac{-2x+(3x+3)-3x}{x(x+1)}$
$=\frac{-2x+3}{x(x+1)}$
a: \(\left(x-5\right)\left(x+5\right)+\left(5-2x\right)^2\)
\(=x^2-25+\left(2x-5\right)^2\)
\(=x^2-25+4x^2-20x+25=5x^2-20x\)
b: ĐKXĐ: \(x\notin\left\{0;-1\right\}\)
\(\dfrac{-2}{x+1}+\dfrac{3}{x}-\dfrac{3x}{x^2+x}\)
\(=\dfrac{-2x+3\left(x+1\right)-3x}{\left(x+1\right)\cdot x}\)
\(=\dfrac{-2x+3x+3-3x}{\left(x+1\right)\cdot x}=\dfrac{-2x+3}{x\left(x+1\right)}\)
