a) 3+\(\left|x+7\right|\) =4
\(\left|x+7\right|\) =4-3
\(\left|x+7\right|\) =1
\(\Rightarrow\)x+7=1 hoặc x+7 =-1
✽ x+7=1 \(\Rightarrow\)x=-6
✽x+7 =-1\(\Rightarrow\)x=-8
Vậy x=-6, x=-8
b) 12-\(\left|x+8\right|\)= 10
\(\left|x+8\right|\) = 12- 10
\(\left|x+8\right|\) = 2
\(\Rightarrow\) x+8 = 2 hoặc x+8 = -2
✽ x+8= 2 \(\Rightarrow\)x=6
✽x+8 = -2 \(\Rightarrow\)x=-10