B. TỰ LUẬN (3,0 điểm)
Hướng dẫn giải
a) \(\frac{1}{6} - 0,4.\frac{5}{8} + \frac{1}{2}\) \( = \frac{1}{6} - \frac{2}{5}.\frac{5}{8} + \frac{1}{2}\) \( = \frac{1}{6} - \frac{1}{4} + \frac{1}{2}\) \( = \frac{2}{{12}} - \frac{3}{{12}} + \frac{6}{{12}}\) \( = \frac{5}{{12}}\). | b) \({\left( {\frac{2}{3}} \right)^3} - 4.{\left( { - 1\frac{3}{4}} \right)^2} + {\left( { - \frac{2}{3}} \right)^3}\) \( = \frac{8}{{27}} - 4.{\left( { - \frac{7}{4}} \right)^2} + \left( { - \frac{8}{{27}}} \right)\) \( = \frac{8}{{27}} - 4.\frac{{49}}{{16}} - \frac{8}{{27}}\) \( = \left( {\frac{8}{{27}} - \frac{8}{{27}}} \right) - \frac{{49}}{4}\) \( = 0 - \frac{{49}}{4}\) \( = - \frac{{49}}{4}.\) | c) \(\sqrt {0,36} .\frac{5}{4} - \sqrt {\frac{{25}}{{16}}} .{\left( {0,8} \right)^2}\) \( = \sqrt {{{\left( {0,6} \right)}^2}} .\frac{5}{4} - \sqrt {{{\left( {\frac{5}{4}} \right)}^2}} .0,64\) \( = 0,6.\frac{5}{4} - \frac{5}{4}.0,64\) \( = \frac{5}{4}.\left( {0,6 - 0,64} \right)\) \( = \frac{5}{4}.\left( { - 0,04} \right)\) \( = \frac{5}{4}.\left( { - \frac{1}{{25}}} \right)\) \( = - \frac{1}{{20}}\). |