Toán Tìm x, biết : a, 28+2x= 35-(-13) b, 21-(29+ 4x) = -12 c, |3x +9|-15 =27 20/07/2021 By Daisy Tìm x, biết : a, 28+2x= 35-(-13) b, 21-(29+ 4x) = -12 c, |3x +9|-15 =27
a, 28+2x= 35-(-13) ⇒28+2x=48 ⇒2x=20 ⇒x=10 b, 21-(29+ 4x) = -12 ⇒29+4x=33 ⇒4x=4 ⇒x=1 c, |3x +9|-15 =27 ⇒|3x+9|=42 ⇒\(\left[ \begin{array}{l}3x+9=42\\3x+9=-42\end{array} \right.\) =>\(\left[ \begin{array}{l}3x=33\\3x=-51\end{array} \right.\) =>\(\left[ \begin{array}{l}x=11\\x=-17\end{array} \right.\) Vậy x=11 hoặc x=-17 Trả lời
$a) 28+2x=35-(-13)$ $28+2x=48$ $2x=48-28$ $2x=20$ $x=20:2$ $→ x=10$ $\textrm{Vậy x=10}$ $b) 21-(29+4x)=-12$ $29+4x=21-(-12)$ $29+4x=33$ $4x=33-29$ $4x=4$ $x=4:4$ $→ x=1$ $\textrm{Vậy x=1}$ $c) |3x+9|-15=27$ $|3x+9|=27+15$ $|3x+9|=42$ $TH1: 3x+9=42$ $3x=42-9$ $3x=33$ $x=33:3$ $→ x=11$ $TH2: 3x+9=-42$ $3x=(-42)-9$ $3x=51$ $x=51:3$ $→ x=-17$ $\textrm{Vậy x=11 hoặc x=-17}$ Trả lời