1. Tim x: | |3x+1|-11 |=3. Cac ban giup minh nhe.Thank you cac ban nhieu Mong cac ban giai chi tiet voi a.

$\text { Đáp án: }$

$\text { | |3x + 1| – 11 | = 3 }$

$\text { => |3x + 1| – 11 = 3 hoặc |3x + 1| – 11 = –3 }$

$\text { TH1: |3x + 1| – 11 = 3 }$

$\text { => |3x + 1| = 3 + 11 }$

$\text { => |3x + 1| = 14 }$

$\text { => 3x + 1 = 14 hoặc 3x + 1 = –14 }$

$\text { => 3x = 14 – 1      | => 3x = –14 – 1 }$

$\text { => 3x = 13            | => 3x = –15 }$

$\text { => x = }$ $\frac {13}{3}$           $\text { | => x = –5 }$

$\text { TH2: |3x + 1| – 11 = –3 }$

$\text { => |3x + 1| = –3 + 11 }$

$\text { => |3x + 1| = 8 }$

$\text { => 3x + 1 = 8 hoặc 3x + 1 = –8 }$

$\text { => 3x = 8 – 1      | => 3x = –8 – 1 }$

$\text { => 3x = 7            | => 3x = –9 }$

$\text { => x = }$ $\frac {7}{3}$            $\text { | => x = –3 }$

$\text { Vậy x = }$ $\frac {13}{3}$ $ ; $ $\frac {7}{3}$ $ ; $ $\text {–5}$ $ ; $ $\text {–3}$ $.$