Advertisements (Quảng cáo)
Làm các phép tính sau:
a)\({{4xy – 5} \over {10{x^3}y}} – {{6{y^2} – 5} \over {10{x^3}y}};\)
b)\({{7x + 6} \over {2x\left( {x + 7} \right)}} – {{3x + 6} \over {2{x^2} + 14x}}\)
Hướng dẫn làm bài:
a)\({{4xy – 5} \over {10{x^3}y}} – {{6{y^2} – 5} \over {10{x^3}y}} = {{4xy – 5 – \left( {6{y^2} – 5} \right)} \over {10{x^3}y}}\)
\( = {{4xy – 5 – 6{y^2} + 5} \over {10{x^3}y}} = {{4xy – 6{y^2}} \over {10{x^3}y}}\)
Advertisements (Quảng cáo)
\( = {{2y\left( {2x – 3y} \right)} \over {10{x^3}y}} = {{2x – 3y} \over {5{x^3}}}\)
b)\({{7x + 6} \over {2x\left( {x + 7} \right)}} – {{3x + 6} \over {2{x^2} + 14x}} = {{7x + 6} \over {2x\left( {x + 7} \right)}} + {{ – \left( {3x + 6} \right)} \over {2x\left( {x + 7} \right)}}\)
\( = {{7x + 6 – 3x – 6} \over {2x\left( {x + 7} \right)}} = {{4x} \over {2x\left( {x + 7} \right)}} = {2 \over {x + 7}}\)