Advertisements (Quảng cáo)
Tìm x ∈ Q, biết rằng:
\(a){{11} \over {12}} – \left( {{2 \over 5} + x} \right) = {2 \over 3}\)
\(b)2{\rm{x}}.\left( {x – {1 \over 7}} \right) = 0\)
\(c){3 \over 4} + {1 \over 4}:x = {2 \over 5}\)
\(a){{11} \over {12}} – \left( {{2 \over 5} + x} \right) = {2 \over 3} \Leftrightarrow \left( {{2 \over 5} + x} \right) = {{11} \over {12}} – {2 \over 3}\)
\( \Leftrightarrow {2 \over 5} + x = {{11} \over {12}} – {8 \over {12}} \Leftrightarrow {2 \over 5} + x = {1 \over 4}\)
Advertisements (Quảng cáo)
\(\Rightarrow x = {1 \over 4} – {2 \over 5} \Leftrightarrow x = {5 \over {20}} – {8 \over {20}} \Leftrightarrow x = – {3 \over {20}}\)
\(b)2{\rm{x}}.\left( {x – {1 \over 7}} \right) = 0 \Leftrightarrow 2{\rm{x}} = 0\) hoặc \({\rm{x}} – {1 \over 7} = 0\)
\(\Rightarrow x = 0\) hoặc \(x = {1 \over 7}\). Vậy x = 0 hoặc \(x = {1 \over 7}\)
\(c){3 \over 4} + {1 \over 4}:x = {2 \over 5} \Leftrightarrow {1 \over 4}:x = {2 \over 5} – {3 \over 4} \Leftrightarrow {1 \over 4}:x = {8 \over {20}} – {{15} \over {20}}\)
\({1 \over 4}:x = {{ – 7} \over {20}} \Leftrightarrow x = {1 \over 4}:{{ – 7} \over {20}} \Leftrightarrow x = {1 \over 4}.{{ – 20} \over 7} = {{ – 5} \over 7}\)