PHẦN II. TỰ LUẬN (7,0 điểm)

(1,5 điểm) Tính giá trị của các biểu thức sau (tính hợp lí nếu có thể):

a) \(\frac{4}{5} + \frac{3}{5}.\left( { - \frac{2}{{15}}} \right)\);                                        

b) \(\sqrt {\frac{{49}}{{81}}} - \left| {\frac{{ - 7}}{3}} \right|\);                             

c) \(\left( { - \frac{3}{4} + \frac{5}{{13}}} \right).\frac{7}{2} - \left( {\frac{9}{4} - \frac{8}{{13}}} \right).\frac{7}{2}\).

a) \(\frac{4}{5} + \frac{3}{5}.\left( { - \frac{2}{{15}}} \right) = \frac{4}{5} + \frac{{ - 2}}{{25}} = \frac{{20}}{{25}} + \frac{{ - 2}}{{25}} = \frac{{18}}{{25}}\).

b) \(\sqrt {\frac{{49}}{{81}}} - \left| {\frac{{ - 7}}{3}} \right| = \frac{7}{9} - \frac{7}{3} = \frac{{21}}{{27}} - \frac{{63}}{{27}} = \frac{{ - 42}}{{27}} = - \frac{{14}}{9}\).

c) \(\left( { - \frac{3}{4} + \frac{5}{{13}}} \right).\frac{7}{2} - \left( {\frac{9}{4} - \frac{8}{{13}}} \right).\frac{7}{2}\)\( = \frac{7}{2}.\left( { - \frac{3}{4} + \frac{5}{{13}} - \frac{9}{4} + \frac{8}{{13}}} \right)\)

\( = \frac{7}{2}.\left[ {\left( { - \frac{3}{4} - \frac{9}{4}} \right) + \left( {\frac{5}{{13}} + \frac{8}{{13}}} \right)} \right]\)\( = \frac{7}{2}.\left[ { - 3 + 1} \right] = \frac{7}{2}.\left( { - 2} \right) = - 7\).