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三、计算。
1. 直接写出得数。
$\dfrac{7}{10}+\dfrac{13}{10}=$ $\dfrac{7}{9}-\dfrac{4}{9}=$ $3-\dfrac{1}{3}=$ $1-\dfrac{1}{6}-\dfrac{1}{6}=$
$1-\dfrac{5}{7}=$ $\dfrac{1}{3}+\dfrac{1}{2}=$ $\dfrac{4}{7}-\dfrac{1}{5}=$ $\dfrac{1}{9}+\dfrac{5}{9}-\dfrac{5}{9}=$
1. 直接写出得数。
$\dfrac{7}{10}+\dfrac{13}{10}=$ $\dfrac{7}{9}-\dfrac{4}{9}=$ $3-\dfrac{1}{3}=$ $1-\dfrac{1}{6}-\dfrac{1}{6}=$
$1-\dfrac{5}{7}=$ $\dfrac{1}{3}+\dfrac{1}{2}=$ $\dfrac{4}{7}-\dfrac{1}{5}=$ $\dfrac{1}{9}+\dfrac{5}{9}-\dfrac{5}{9}=$
答案
$\dfrac{7}{10}+\dfrac{13}{10}=2$；$\dfrac{7}{9}-\dfrac{4}{9}=\dfrac{1}{3}$；$3-\dfrac{1}{3}=2\dfrac{2}{3}$；$1-\dfrac{1}{6}-\dfrac{1}{6}=\dfrac{2}{3}$；$1-\dfrac{5}{7}=\dfrac{2}{7}$；$\dfrac{1}{3}+\dfrac{1}{2}=\dfrac{5}{6}$；$\dfrac{4}{7}-\dfrac{1}{5}=\dfrac{13}{35}$；$\dfrac{1}{9}+\dfrac{5}{9}-\dfrac{5}{9}=\dfrac{1}{9}$
2. 计算下面各题。
$\dfrac{23}{20}+\dfrac{1}{7}+\dfrac{17}{20}$ $\dfrac{5}{6}-\dfrac{3}{4}+\dfrac{1}{6}$ $\dfrac{5}{4}-\dfrac{3}{7}-\dfrac{4}{7}$
$1-(\dfrac{5}{6}-\dfrac{2}{9})$ $\dfrac{19}{11}-(\dfrac{8}{11}+\dfrac{1}{3})$ $\dfrac{12}{13}-(\dfrac{3}{5}-\dfrac{1}{13})-\dfrac{2}{5}$
$\dfrac{23}{20}+\dfrac{1}{7}+\dfrac{17}{20}$ $\dfrac{5}{6}-\dfrac{3}{4}+\dfrac{1}{6}$ $\dfrac{5}{4}-\dfrac{3}{7}-\dfrac{4}{7}$
$1-(\dfrac{5}{6}-\dfrac{2}{9})$ $\dfrac{19}{11}-(\dfrac{8}{11}+\dfrac{1}{3})$ $\dfrac{12}{13}-(\dfrac{3}{5}-\dfrac{1}{13})-\dfrac{2}{5}$
答案
第一题：$\dfrac{23}{20}+\dfrac{1}{7}+\dfrac{17}{20}$
解：
$\dfrac{23}{20}+\dfrac{17}{20}+\dfrac{1}{7}$
$=\dfrac{40}{20}+\dfrac{1}{7}$
$=2+\dfrac{1}{7}$
$=2\dfrac{1}{7}$
第二题：$\dfrac{5}{6}-\dfrac{3}{4}+\dfrac{1}{6}$
解：
$\dfrac{5}{6}+\dfrac{1}{6}-\dfrac{3}{4}$
$=1-\dfrac{3}{4}$
$=\dfrac{1}{4}$
第三题：$\dfrac{5}{4}-\dfrac{3}{7}-\dfrac{4}{7}$
解：
$\dfrac{5}{4}-(\dfrac{3}{7}+\dfrac{4}{7})$
$=\dfrac{5}{4}-1$
$=\dfrac{1}{4}$
第四题：$1-(\dfrac{5}{6}-\dfrac{2}{9})$
解：
$1-(\dfrac{15}{18}-\dfrac{4}{18})$
$=1-\dfrac{11}{18}$
$=\dfrac{7}{18}$
第五题：$\dfrac{19}{11}-(\dfrac{8}{11}+\dfrac{1}{3})$
解：
$\dfrac{19}{11}-\dfrac{8}{11}-\dfrac{1}{3}$
$=1-\dfrac{1}{3}$
$=\dfrac{2}{3}$
第六题：$\dfrac{12}{13}-(\dfrac{3}{5}-\dfrac{1}{13})-\dfrac{2}{5}$
解：
$\dfrac{12}{13}-\dfrac{3}{5}+\dfrac{1}{13}-\dfrac{2}{5}$
$=(\dfrac{12}{13}+\dfrac{1}{13})-(\dfrac{3}{5}+\dfrac{2}{5})$
$=1-1$
$=0$
解：
$\dfrac{23}{20}+\dfrac{17}{20}+\dfrac{1}{7}$
$=\dfrac{40}{20}+\dfrac{1}{7}$
$=2+\dfrac{1}{7}$
$=2\dfrac{1}{7}$
第二题：$\dfrac{5}{6}-\dfrac{3}{4}+\dfrac{1}{6}$
解：
$\dfrac{5}{6}+\dfrac{1}{6}-\dfrac{3}{4}$
$=1-\dfrac{3}{4}$
$=\dfrac{1}{4}$
第三题：$\dfrac{5}{4}-\dfrac{3}{7}-\dfrac{4}{7}$
解：
$\dfrac{5}{4}-(\dfrac{3}{7}+\dfrac{4}{7})$
$=\dfrac{5}{4}-1$
$=\dfrac{1}{4}$
第四题：$1-(\dfrac{5}{6}-\dfrac{2}{9})$
解：
$1-(\dfrac{15}{18}-\dfrac{4}{18})$
$=1-\dfrac{11}{18}$
$=\dfrac{7}{18}$
第五题：$\dfrac{19}{11}-(\dfrac{8}{11}+\dfrac{1}{3})$
解：
$\dfrac{19}{11}-\dfrac{8}{11}-\dfrac{1}{3}$
$=1-\dfrac{1}{3}$
$=\dfrac{2}{3}$
第六题：$\dfrac{12}{13}-(\dfrac{3}{5}-\dfrac{1}{13})-\dfrac{2}{5}$
解：
$\dfrac{12}{13}-\dfrac{3}{5}+\dfrac{1}{13}-\dfrac{2}{5}$
$=(\dfrac{12}{13}+\dfrac{1}{13})-(\dfrac{3}{5}+\dfrac{2}{5})$
$=1-1$
$=0$
3. 解方程。
$x-\dfrac{3}{4}=\dfrac{1}{12}$ $\dfrac{5}{6}-x=\dfrac{1}{9}$ $x+\dfrac{7}{10}=\dfrac{4}{5}$
$x-\dfrac{3}{4}=\dfrac{1}{12}$ $\dfrac{5}{6}-x=\dfrac{1}{9}$ $x+\dfrac{7}{10}=\dfrac{4}{5}$
答案
解方程：
1. $ x - \dfrac{3}{4} = \dfrac{1}{12} $
解：$ x = \dfrac{1}{12} + \dfrac{3}{4} $
$ x = \dfrac{1}{12} + \dfrac{9}{12} $
$ x = \dfrac{10}{12} = \dfrac{5}{6} $
2. $ \dfrac{5}{6} - x = \dfrac{1}{9} $
解：$ x = \dfrac{5}{6} - \dfrac{1}{9} $
$ x = \dfrac{15}{18} - \dfrac{2}{18} $
$ x = \dfrac{13}{18} $
3. $ x + \dfrac{7}{10} = \dfrac{4}{5} $
解：$ x = \dfrac{4}{5} - \dfrac{7}{10} $
$ x = \dfrac{8}{10} - \dfrac{7}{10} $
$ x = \dfrac{1}{10} $
1. $ x - \dfrac{3}{4} = \dfrac{1}{12} $
解：$ x = \dfrac{1}{12} + \dfrac{3}{4} $
$ x = \dfrac{1}{12} + \dfrac{9}{12} $
$ x = \dfrac{10}{12} = \dfrac{5}{6} $
2. $ \dfrac{5}{6} - x = \dfrac{1}{9} $
解：$ x = \dfrac{5}{6} - \dfrac{1}{9} $
$ x = \dfrac{15}{18} - \dfrac{2}{18} $
$ x = \dfrac{13}{18} $
3. $ x + \dfrac{7}{10} = \dfrac{4}{5} $
解：$ x = \dfrac{4}{5} - \dfrac{7}{10} $
$ x = \dfrac{8}{10} - \dfrac{7}{10} $
$ x = \dfrac{1}{10} $
1. 图形
绕点$O$逆时针旋转$90^{\circ}$得到()。
A.
B.
C.
绕点$O$逆时针旋转$90^{\circ}$得到()。A.
B.
C.
答案
C
