a) Ta có: \(P = \frac{{{x^2} + 6{\rm{x}} + 9}}{{{x^2} + 3{\rm{x}}}} = \frac{{{{\left( {x + 3} \right)}^2}}}{{x\left( {x + 3} \right)}} = \frac{{x + 3}}{x}\)
\(Q = \frac{{{x^2} + 3{\rm{x}}}}{{{x^2} - 9}} = \frac{{x\left( {x + 3} \right)}}{{\left( {x - 3} \right)\left( {x + 3} \right)}} = \frac{x}{{x - 3}}\)
b) Ta có:
\(P.Q = \frac{{x + 3}}{x}.\frac{x}{{x - 3}} = \frac{{\left( {x + 3} \right).x}}{{x.\left( {x - 3} \right)}} = \frac{{x + 3}}{{x - 3}}\)
\(P:Q = \frac{{x + 3}}{x}:\frac{x}{{x - 3}} = \frac{{x + 3}}{x}.\frac{{x - 3}}{x} = \frac{{{x^2} - 9}}{{{x^2}}}\)
