$Bài 1:$
$13-98+91-75+98-91-13$
$=(13-13)+(91-91)+(98-98)-75$
$=0+0+0-75$
$=-75$
$5-(48-703+125)+(48-703+12)+125$
$=5-48+703-125+48-703+12+125$
$=5+(-48+48)+(703-703)+(-125+125)+12$
$=5+0+0+0+12$
$=17$
$-5-{-[-(-7)+(-10)]-[5-(-12)]}-[(-3)-(-9)-(+4)-5]$
$=-5-[-(7-10)-(5+12)]-(-3+9-4-5)$
$=-5-(-7+10-5-12)+3-9+4+5$
$=-5+7-10+5+12+3-9+4+5$
$=(-5+5)+(5+4-9)+(7+3-10)+12$
$=0+0+0+12$
$=12$
$7-{12-[-(-3)+(-10)-(-11)]-[-(-9)+(-8)-(+12)]}-(-4)$
$=7-[12-(3-10+11)-(9-8-12)]+4$
$=7-(12-3+10-11-9+8+12)+4$
$=7-12+3-10+11+9-8-12+4$
$=(7+3-10)-(12+12)+11+4-8+9$
$=0-24+11+4-8+9$
$=-8$
$Bài 2 :$
$0<|x+1| ≤3$
$⇒|x+1|∈{1;2;3}$
$+)|x+1|=1⇒$\(\left[ \begin{array}{l}x+1=1\\x+1=-1\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=0\\x=-2\end{array} \right.\)
$+)|x+1|=2⇒$\(\left[ \begin{array}{l}x+1=2\\x+1=-2\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=1\\x=-3\end{array} \right.\)
$+)|x+1|=3 ⇒$ \(\left[ \begin{array}{l}x+1=3\\x+1=-3\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=2\\x=-4\end{array} \right.\)
$Vậy$ $x =...$
-(5+x-3)-|-4|=5+7-4
$⇔-5-x+3-4=8$
$⇔-5-x-1=8$
$⇔-6-x=8$
$⇔-x=8+6$
$⇔-x=14$
$⇒x=-14$
$vậy$ $x=-14$
