各数大小关系为：$-(+4.5) ＜ -3\dfrac{1}{5} ＜ 0 ＜ 1 ＜ 5；$它们的相反数分别为$-5，$$3\dfrac{1}{5}，$$-1，$$0，$$4.5，$在数轴上表示如下：
$−3²，0，12，−|−12|，−(−1)$ $-3^2,-3.12,-|-12|,-\dfrac{\pi}{2}$
解：原式$=4\times5 - 1=20 - 1=19$
解：$\because\left|-\dfrac{6}{7}\right|=\dfrac{6}{7}=\dfrac{48}{56}，$$\left|-\dfrac{7}{8}\right|=\dfrac{7}{8}=\dfrac{49}{56}，$$\dfrac{48}{56}＜\dfrac{49}{56}，$$\therefore-\dfrac{6}{7}＞-\dfrac{7}{8}$
解： (2)$-|-3|=-3，$$-[-(-1)]=-1，$$\because-3 ＜ -1，$$\therefore-|-3| ＜ -[-(-1)]$
解： (3)$-\dfrac{1}{2}=-\dfrac{5}{10}，$$-\dfrac{2}{5}=-\dfrac{4}{10}，$$-\dfrac{7}{10}=-\dfrac{7}{10}，$$\because\left|-\dfrac{7}{10}\right|＞\left|-\dfrac{5}{10}\right|＞\left|-\dfrac{4}{10}\right|，$$\therefore-\dfrac{7}{10}＜-\dfrac{1}{2}＜-\dfrac{2}{5}$
解：$\because a,b$互为相反数，$\therefore a + b=0；$$\because|m|=5，$$\therefore|m|=5；$$\because n$是最大的负整数，$\therefore n=-1。$原式$=99\times0 + 5 - (-1)=0 + 5 + 1=6$
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