Thực hiện phép tính đã chỉ ra:
\(a)\frac{1}{{xy}} + \frac{1}{{yz}} + \frac{1}{{z{\rm{x}}}}\)
\(b)\frac{x}{{2{\rm{x}} - y}} + \frac{y}{{2{\rm{x}} + y}} + \frac{{3{\rm{x}}y}}{{{y^2} - 4{{\rm{x}}^2}}}\)
Thực hiện theo quy tắc cộng hai phân thức
\(a)\frac{1}{{xy}} + \frac{1}{{yz}} + \frac{1}{{z{\rm{x}}}} = \frac{z}{{xyz}} + \frac{x}{{xyz}} + \frac{y}{{xyz}} = \frac{{z + x + y}}{{xyz}}\)
\(\begin{array}{l}b)\frac{x}{{2{\rm{x}} - y}} + \frac{y}{{2{\rm{x}} + y}} + \frac{{3{\rm{x}}y}}{{{y^2} - 4{{\rm{x}}^2}}}\\ = \frac{x}{{2{\rm{x}} - y}} + \frac{y}{{2{\rm{x}} + y}} - \frac{{3{\rm{x}}y}}{{4{{\rm{x}}^2} - {y^2}}}\\ = \frac{{x\left( {2{\rm{x}} + y} \right) + y\left( {2{\rm{x}} - y} \right) - 3{\rm{x}}y}}{{\left( {2{\rm{x}} - y} \right)\left( {2{\rm{x}} + y} \right)}}\\ = \frac{{2{{\rm{x}}^2} + xy + 2{\rm{x}}y - {y^2} - 3{\rm{x}}y}}{{\left( {2{\rm{x}} - y} \right)\left( {2{\rm{x}} + y} \right)}} = \frac{{2{{\rm{x}}^2} - {y^2}}}{{\left( {2{\rm{x}} - y} \right)\left( {2{\rm{x}} + y} \right)}}\end{array}\)