Biểu thức \(A = \left( { - \frac{3}{4} + \frac{2}{5}} \right):\frac{3}{7} + \left( {\frac{3}{5} + \frac{{ - 1}}{4}} \right):\frac{3}{7}\) có giá trị là:

Đáp án đúng là: A

Ta có:

\(A = \left( { - \frac{3}{4} + \frac{2}{5}} \right):\frac{3}{7} + \left( {\frac{3}{5} + \frac{{ - 1}}{4}} \right):\frac{3}{7}\)

\(A = \left( { - \frac{3}{4} + \frac{2}{5}} \right).\frac{7}{3} + \left( {\frac{3}{5} + \frac{{ - 1}}{4}} \right).\frac{7}{3}\)

\[A = \left( { - \frac{3}{4} + \frac{2}{5} + \frac{3}{5} + \frac{{ - 1}}{4}} \right).\frac{7}{3}\]

\[A = \left[ {\left( { - \frac{3}{4} + \frac{{ - 1}}{4}} \right) + \left( {\frac{2}{5} + \frac{3}{5}} \right)} \right].\frac{7}{3}\]

\[A = \left[ {\frac{0}{4} + \frac{0}{5}} \right].\frac{7}{3}\]

\(A = 0.\frac{7}{3}\)

A = 0.

Vậy A = 0.