Câu 11:
a, $-29-9.(2x-1)²=-110$
⇔ $9.(2x-1)²=81$
⇔ $(2x-1)²=9$
⇔ \(\left[ \begin{array}{l}2x-1=3\\2x-1=-3\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=2\\x=-1\end{array} \right.\)
b, $-2.(-x-5)+28=20-3.(x+4)$
⇔ $2x+10+28=20-3x-12$
⇔ $5x=-30$
⇔ $x=-6$
Câu 12:
$S=-(a-b-c)+(-c+b+a)-(a+b)$
= $-a+b+c-c+b+a-a-b$
= $-a+b$
= $-(a-b)$
= $-(-1)$
= $1$
Câu 13:
a, $x²+2x+4$⋮ $x+1$
⇔ $(x+1)²+3$⋮ $x+1$
⇒ $x+1∈Ư(3)=\{-3;-1;1;3\}$
⇔ $x∈\{-4;-2;0;1\}$
b, $5x+47y$
= $5x+30y+17y$
= $5.(x+6y)+17y$
Mà $17y$⋮ $17$
⇒ $5.(x+6y)$⋮ $17$
⇒ $x+6y$⋮ $17$