Question

绝对值不等式公式法

| f(x) | > g(x) 推出？？反推也可以的
| f(x) | < g(x) 呢

Answer 1

| f(x) | > g(x)

所以 f(x) > g(x) 或 f(x) ＜-g(x)

| f(x) | < g(x)

所以- g(x)＜f(x) ＜g(x)

Answer 2

| f(x) | > g(x) <=>f(x)>g(x)或f(x)<-g(x)

|f(x)|<g(x)<=>-g(x)<f(x)<g(x)