1. 阅读下列计算过程:
计算:$-5\frac{5}{6}-9\frac{2}{3}+17\frac{3}{4}-3\frac{1}{2}$.
解:原式$=(-5-\frac{5}{6})+(-9-\frac{2}{3})+(17+\frac{3}{4})+(-3-\frac{1}{2})= [(-5)+(-9)+(-3)+17]+[(-\frac{5}{6})+(-\frac{2}{3})+(-\frac{1}{2})+\frac{3}{4}]= 0+(-1\frac{1}{4})= -\frac{5}{4}$.
上述方法叫作拆项法,灵活运用加法的交换律、结合律可使运算简便.
仿照上面的方法计算:$-2023\frac{2}{3}-2024\frac{5}{6}+4304-\frac{1}{2}$.
计算:$-5\frac{5}{6}-9\frac{2}{3}+17\frac{3}{4}-3\frac{1}{2}$.
解:原式$=(-5-\frac{5}{6})+(-9-\frac{2}{3})+(17+\frac{3}{4})+(-3-\frac{1}{2})= [(-5)+(-9)+(-3)+17]+[(-\frac{5}{6})+(-\frac{2}{3})+(-\frac{1}{2})+\frac{3}{4}]= 0+(-1\frac{1}{4})= -\frac{5}{4}$.
上述方法叫作拆项法,灵活运用加法的交换律、结合律可使运算简便.
仿照上面的方法计算:$-2023\frac{2}{3}-2024\frac{5}{6}+4304-\frac{1}{2}$.
答案:$-2023\frac{2}{3}-2024\frac{5}{6}+4304-\frac{1}{2}$
$=(-2023-\frac{2}{3})+(-2024-\frac{5}{6})+(4304-\frac{1}{2})$
$=[(-2023)+(-2024)+4304]+[(-\frac{2}{3})+(-\frac{5}{6})-$
$\frac{1}{2}]=257+(-2)=255.$
$=(-2023-\frac{2}{3})+(-2024-\frac{5}{6})+(4304-\frac{1}{2})$
$=[(-2023)+(-2024)+4304]+[(-\frac{2}{3})+(-\frac{5}{6})-$
$\frac{1}{2}]=257+(-2)=255.$
2. 阅读下面的计算过程:
计算:$\frac{1}{1×2}+\frac{1}{2×3}+\frac{1}{3×4}+…+\frac{1}{9×10}$.
解:因为$\frac{1}{1×2}= 1-\frac{1}{2}$,$\frac{1}{2×3}= \frac{1}{2}-\frac{1}{3}$,$\frac{1}{3×4}= \frac{1}{3}-\frac{1}{4}$,…,$\frac{1}{9×10}= \frac{1}{9}-\frac{1}{10}$,
所以原式$=(1-\frac{1}{2})+(\frac{1}{2}-\frac{1}{3})+(\frac{1}{3}-\frac{1}{4})+…+(\frac{1}{9}-\frac{1}{10})= 1+(-\frac{1}{2}+\frac{1}{2})+(-\frac{1}{3}+\frac{1}{3})+…+(-\frac{1}{9}+\frac{1}{9})-\frac{1}{10}= 1-\frac{1}{10}= \frac{9}{10}$.
根据以上解决问题的方法计算:
$-\frac{1}{2}-\frac{1}{6}-\frac{1}{12}-\frac{1}{20}-\frac{1}{30}-\frac{1}{42}$.
计算:$\frac{1}{1×2}+\frac{1}{2×3}+\frac{1}{3×4}+…+\frac{1}{9×10}$.
解:因为$\frac{1}{1×2}= 1-\frac{1}{2}$,$\frac{1}{2×3}= \frac{1}{2}-\frac{1}{3}$,$\frac{1}{3×4}= \frac{1}{3}-\frac{1}{4}$,…,$\frac{1}{9×10}= \frac{1}{9}-\frac{1}{10}$,
所以原式$=(1-\frac{1}{2})+(\frac{1}{2}-\frac{1}{3})+(\frac{1}{3}-\frac{1}{4})+…+(\frac{1}{9}-\frac{1}{10})= 1+(-\frac{1}{2}+\frac{1}{2})+(-\frac{1}{3}+\frac{1}{3})+…+(-\frac{1}{9}+\frac{1}{9})-\frac{1}{10}= 1-\frac{1}{10}= \frac{9}{10}$.
根据以上解决问题的方法计算:
$-\frac{1}{2}-\frac{1}{6}-\frac{1}{12}-\frac{1}{20}-\frac{1}{30}-\frac{1}{42}$.
答案:原式$=-\frac{1}{1×2}-\frac{1}{2×3}-\frac{1}{3×4}-\frac{1}{4×5}-\frac{1}{5×6}-\frac{1}{6×7}=$
$-(1-\frac{1}{2})-(\frac{1}{2}-\frac{1}{3})-(\frac{1}{3}-\frac{1}{4})-(\frac{1}{4}-\frac{1}{5})-$
$(\frac{1}{5}-\frac{1}{6})-(\frac{1}{6}-\frac{1}{7})=-1+\frac{1}{7}=-\frac{6}{7}.$
$-(1-\frac{1}{2})-(\frac{1}{2}-\frac{1}{3})-(\frac{1}{3}-\frac{1}{4})-(\frac{1}{4}-\frac{1}{5})-$
$(\frac{1}{5}-\frac{1}{6})-(\frac{1}{6}-\frac{1}{7})=-1+\frac{1}{7}=-\frac{6}{7}.$
3. (2024·辽宁鞍山期末)在小学,我们学习过交换律、结合律以及乘法分配律,利用这些运算律可以使一些数学问题简化,例如:$(\frac{1}{4}+\frac{1}{6}-\frac{1}{2})×12= \frac{1}{4}×12+\frac{1}{6}×12-\frac{1}{2}×12= 3+2-6= -1$,
请利用运算律解决下列问题:
计算:$(-\frac{6}{5})×(-\frac{2}{3})+(-\frac{6}{5})×(+\frac{17}{3})$.
请利用运算律解决下列问题:
计算:$(-\frac{6}{5})×(-\frac{2}{3})+(-\frac{6}{5})×(+\frac{17}{3})$.
答案:$(-\frac{6}{5})×(-\frac{2}{3})+(-\frac{6}{5})×(+\frac{17}{3})$
$=(-\frac{6}{5})×(-\frac{2}{3}+\frac{17}{3})=-\frac{6}{5}×5=-6.$
$=(-\frac{6}{5})×(-\frac{2}{3}+\frac{17}{3})=-\frac{6}{5}×5=-6.$
4. 计算:$(\frac{3}{8}-\frac{1}{6}+\frac{5}{12})÷(-\frac{1}{24})$.
答案:原式$=(\frac{3}{8}-\frac{1}{6}+\frac{5}{12})×(-24)$
$=\frac{3}{8}×(-24)-\frac{1}{6}×(-24)+\frac{5}{12}×(-24)$
$=-9+4-10=-15.$
$=\frac{3}{8}×(-24)-\frac{1}{6}×(-24)+\frac{5}{12}×(-24)$
$=-9+4-10=-15.$