Question

17．解方程．
$\begin{array}{l}\frac{7}{8}\end{array}$x=$\begin{array}{l}\frac{5}{24}\end{array}$
x÷$\begin{array}{l}\frac{5}{18}\end{array}$=$\begin{array}{l}\frac{42}{25}\end{array}$
x-$\begin{array}{l}\frac{1}{5}\end{array}$x=16．

Answer 1

分析 ①依據(jù)等式的性質(zhì)，方程兩邊同時減去15，再同時除以0.6求解；
②依據(jù)等式的性質(zhì)，方程兩邊同時乘$\frac{5}{18}$求解；
③先化簡左邊，依據(jù)等式的性質(zhì)，方程兩邊同時乘$\frac{5}{4}$求解．

解答 解：①$\begin{array}{l}\frac{7}{8}\end{array}$x=$\begin{array}{l}\frac{5}{24}\end{array}$
      $\begin{array}{l}\frac{7}{8}\end{array}$x×$\frac{8}{7}$=$\begin{array}{l}\frac{5}{24}\end{array}$×$\frac{8}{7}$
              x=$\frac{5}{21}$

  ②x÷$\begin{array}{l}\frac{5}{18}\end{array}$=$\begin{array}{l}\frac{42}{25}\end{array}$
x÷$\begin{array}{l}\frac{5}{18}\end{array}$×$\frac{5}{18}$=$\begin{array}{l}\frac{42}{25}\end{array}$×$\frac{5}{18}$
             x=$\frac{7}{15}$

③x-$\begin{array}{l}\frac{1}{5}\end{array}$x=16
      $\frac{4}{5}$x=16
  $\frac{4}{5}$x×$\frac{5}{4}$=16×$\frac{5}{4}$
          x=20

點評 此題考查了運用等式的性質(zhì)解方程，即等式兩邊同加上或同減去、同乘上或同除以一個數(shù)（0除外），兩邊仍相等，同時注意“=”上下要對齊．