Câu 99: trang 49 sgk toán lớp 7 tập 1
Tính giá trị của các biểu thức sau:
$P=\left ( -0,5-\frac{3}{5} \right )\div (-3)+\frac{1}{3}-\left ( -\frac{1}{6} \right )\div (-2)$;
$Q=\left ( \frac{2}{25}-1,008 \right )\div \frac{4}{7}\div \left [ \left ( 3\frac{1}{4}-6\frac{5}{9} \right ).2\frac{2}{17} \right ]$.
Bài Làm:
$P=\left ( -0,5-\frac{3}{5} \right )\div (-3)+\frac{1}{3}-\left ( -\frac{1}{6} \right )\div (-2)$
$=\left ( -\frac{1}{2}-\frac{3}{5} \right ). \frac{-1}{3}+\frac{1}{3}-\left ( -\frac{1}{6} \right ).\left ( -\frac{1}{2} \right )$
$=\left ( -\frac{5}{10}-\frac{6}{10} \right ). \frac{-1}{3}+\frac{1}{3}-\frac{1}{12}$
$=\frac{-11}{10}. \frac{-1}{3}+\frac{1}{3}-\frac{1}{12}$
$=\frac{11}{30}+\frac{1}{3}-\frac{1}{12}$
$=\frac{22}{60}+\frac{20}{60}-\frac{5}{60}$
$=\frac{37}{60}$
$Q=\left ( \frac{2}{25}-1,008 \right )\div \frac{4}{7}\div \left [ \left ( 3\frac{1}{4}-6\frac{5}{9} \right ).2\frac{2}{17} \right ]$
$=\left ( \frac{80}{1000}- \frac{1008}{1000} \right ).\frac{7}{4}\div \left [ \left ( \frac{13}{4}-\frac{59}{9} \right ).\frac{36}{17} \right ]$
$=\frac{-116}{125}.\frac{7}{4}\div \left ( \frac{-119}{36}.\frac{36}{17} \right )$
$=\frac{-116}{125}.\frac{7}{4}\div (-7)$
$=\frac{-116}{125}.\frac{7}{4}.\frac{-1}{7}$
$=\frac{(-116).7.(-1)}{125.4.7}$
$=\frac{29}{125}$