câu 2: a) tìm số nguyên x biết 218 – ( x + 31 ) = x – 29 b) tìm số nguyên x sao cho -5/2 < 3/x < 2/-3 22/09/2021 Bởi Gianna câu 2: a) tìm số nguyên x biết 218 – ( x + 31 ) = x – 29 b) tìm số nguyên x sao cho -5/2 < 3/x < 2/-3
$\begin{array}{l}a)\ 218-(x+31)=x-29\\\Leftrightarrow 218-x-31=x-29\\\Leftrightarrow -x-x=-29-218+31\\\Leftrightarrow -2x=-216\\\Leftrightarrow x=108\\\,\\b)\ \dfrac{-5}2<\dfrac 3x<\dfrac2{-3}\\\Leftrightarrow \dfrac{(-5).(-6)}{2.(-6)}<\dfrac{10.3}{10x}<\dfrac{15.2}{15.(-3)}\\\Leftrightarrow \dfrac{30}{-12}<\dfrac{30}{10x}<\dfrac{30}{-45}\\\Leftrightarrow -12>10x>-45\\\Leftrightarrow \dfrac{-6}5<x<\dfrac{-9}2\\\Leftrightarrow -1>x>-5\\\text{mà $x\in\mathbb{Z}$}\\\to x\in\{-2;-3;-4\} \end{array}$ Bình luận
$\begin{array}{l}a)\ 218-(x+31)=x-29\\\Leftrightarrow 218-x-31=x-29\\\Leftrightarrow -x-x=-29-218+31\\\Leftrightarrow -2x=-216\\\Leftrightarrow x=108\\\,\\b)\ \dfrac{-5}2<\dfrac 3x<\dfrac2{-3}\\\Leftrightarrow \dfrac{(-5).(-6)}{2.(-6)}<\dfrac{10.3}{10x}<\dfrac{15.2}{15.(-3)}\\\Leftrightarrow \dfrac{30}{-12}<\dfrac{30}{10x}<\dfrac{30}{-45}\\\Leftrightarrow -12>10x>-45\\\Leftrightarrow \dfrac{-6}5<x<\dfrac{-9}2\\\Leftrightarrow -1>x>-5\\\text{mà $x\in\mathbb{Z}$}\\\to x\in\{-2;-3;-4\} \end{array}$