Kiểm tra 15 phút Toán Chương 2 Đại số 8: Rút gọn biểu thức sau

Rút gọn:

1. \(A = {{{a^2} + {b^2}} \over {{x^3} + {x^2}y}}.{{{x^2} – {y^2}} \over {{a^4} – {b^4}}}\)

2. \(B = {{64{x^2}{y^2} – 1} \over {{x^2} – 4}}.{{{{\left( {x + 2} \right)}^2}} \over {{x^2} – 4}}.{{{{\left( {x – 2} \right)}^2}} \over {8xy + 1}}\)

3. \(C = \left( {1 – {{a – b} \over {a + b}}} \right).\left( {2 + {{2b} \over {a – b}}} \right).\)

1. \(A = {{{a^2} + {b^2}} \over {{x^2}\left( {x + y} \right)}}.{{\left( {x – y} \right)\left( {x + y} \right)} \over {\left( {{a^2} + {b^2}} \right)\left( {{a^2} – {b^2}} \right)}} = {{x – y} \over {{x^2}\left( {{a^2} – {b^2}} \right)}}.\)

2.\(B = {{\left( {8xy + 1} \right)\left( {8xy – 1} \right).{{\left( {x + 2} \right)}^2}{{\left( {x – 2} \right)}^2}} \over {{{\left( {x + 2} \right)}^2}{{\left( {x – 2} \right)}^2}\left( {8xy + 1} \right)}} \)\(\;= 8xy – 1.\)

3. \(C = {{a + b – a + b} \over {a + b}}.{{2a – 2b + 2b} \over {a – b}} = {{4ab} \over {{a^2} – {b^2}}}.\)