11.(10分)比较下列各数的大小,并在数轴上把它们的相反数表示出来.
$5,-3\frac {1}{5},1,0,-(+4.5).$
答案：解:$-(+4.5)＜-3\frac{1}{5}＜0＜1＜5$.
5，$-3\frac{1}{5}$,1,0,$-(+4.5)$的相反数分别为-5,$3\frac{1}{5}$,-1,0,4.5，在数轴上表示如答图所示.
12.(10分)把下列各数填入相应的括号中:
$-3^{2},0,12,-3.12,\frac {23}{7},1\frac {3}{4},-|-12|,-\frac {π}{2},-(-1).$
整数:{
$-3^2,0,12,-|-12|,-(-1)$
};
负数:{
$-3^2,-3.12,-|-12|,-\frac{π}{2}$
};
非负整数:{
$0,12,-(-1)$
}.
答案：解:整数:$\{-3^2,0,12,-|-12|,-(-1)\}$;
负数:$\{-3^2,-3.12,-|-12|,-\frac{1}{2}\}$;
非负整数:$\{0,12,-(-1)\}$.
13.(10分)计算:
(1)$-(-4)×|-5|-[-(-1)]$;
(2)$-[-(+8)]-|-8|+2021.$
答案：解:
(1)原式$=4× 5-1=20-1=19$.
(2)原式$=8-8+2021=0+2021=2021$.
14.(10分)比较下列各组数的大小:(要有解答过程)
(1)$-\frac {6}{7}与-\frac {7}{8}$;
(2)$-|-3|与-[-(+1)]$;
(3)$-\frac {1}{2},-\frac {2}{5}与-\frac {7}{10}$.
答案：解:
(1)因为$\left|-\frac{6}{7}\right|=\frac{6}{7}=\frac{48}{56}$,$\left|-\frac{7}{8}\right|=\frac{7}{8}=\frac{49}{56}$,而$\frac{48}{56}＜\frac{49}{56}$,所以$-\frac{6}{7}＞-\frac{7}{8}$.
(2)因为$-|-3|=-3$,$-[-(+1)]=1$,而$-3＜1$,所以$-|-3|＜-[-(+1)]$.
(3)因为$\left|-\frac{1}{2}\right|=\frac{1}{2}=\frac{5}{10}$,$\left|-\frac{2}{5}\right|=\frac{2}{5}=\frac{4}{10}$,$\left|-\frac{7}{10}\right|=\frac{7}{10}$,而$\frac{4}{10}＜\frac{5}{10}＜\frac{7}{10}$,所以$-\frac{7}{10}＜-\frac{1}{2}＜-\frac{2}{5}$.
15.(10分)已知a,b互为相反数,m的绝对值是5,n是最大的负整数,求$99(a+b)+|m|-n$的值.
答案：解:因为a,b互为相反数,m的绝对值是5,n是最大的负整数,所以$a+b=0$,$|m|=5$,$n=-1$,所以原式$=99× 0+5-(-1)=0+5+1=6$.
