|x+3| là giá trị tuyệt đối
\(-20\le\left|x+3\right|\le10\)
\(\Rightarrow\left|x+3\right|\in\left\{0;1;2;3;4;5;6;7;8;9;10\right\}\)
\(\Rightarrow x+3\in\left\{0;\pm1;\pm2;\pm3;\pm4;\pm5;\pm6;\pm7;\pm8;\pm9;\pm10\right\}\)
=> x\(\in\left\{-3;\pm4;\pm5;\pm6;\pm7;\pm8;\pm9;\pm10;\pm11;\pm12;\pm13\right\}\)