Tìm x, biết: 3 - 3x - ( 5/4 - 7/5) = 9/20

7/15

Tìm x, biết: \(3 - 3x - \left( {\frac{5}{4} - \frac{7}{5}} \right) = \frac{9}{{20}}\)

\(x = \frac{9}{{10}}\);

\(x = \frac{{ - 9}}{{10}}\);

\(x = \frac{{10}}{9}\);

\(x = \frac{{ - 10}}{9}\).

Giải thích

Đáp án đúng là: A

\(3 - 3x - \left( {\frac{5}{4} - \frac{7}{5}} \right) = \frac{9}{{20}}\)

\(3 - 3x - \left( {\frac{{ - 3}}{{20}}} \right) = \frac{9}{{20}}\)

\( - 3x = \frac{9}{{20}} + \left( {\frac{{ - 3}}{{20}}} \right) - 3\)

\( - 3x = \frac{6}{{20}} - 3\)

\( - 3x = \frac{3}{{10}} - \frac{{30}}{{10}}\)

\( - 3x = \frac{{ - 27}}{{10}}\)

\(x = \frac{{ - 27}}{{10}}:\left( { - 3} \right)\)

\(x = \frac{9}{{10}}\). Vậy \(x = \frac{9}{{10}}\).