Tìm x thuộc z
a) -1/2
Tìm x thuộc z
a) -1/2
By Piper
By Piper
a) -1/2<x/8<-7/15
*Quy đồng
-1× 60 / 120 < 15x / 120 < -7× 8/ 120
= -60 < 15x < -56
= -4 < x < – 3,7333
Vậy -4 < x < -3,733 ∈ Z
b)-1/3<x/24<-1/4
* Quy đồng :
-1×8/24< x / 24 < -1×6 / 24
⇔ -8 < x < -6
⇒ x =-7
Vậy x= -7 ∈ Z
c)4/21<x/42<2/7
*Quy đồng :
4× 2/ 42 < x/42 < 7×2/ 42
⇔ 8 < x < 14
Vậy x từ { 9; 10;11;12;13 }
d)-1/2<x/30<-1/5
*Quy đồng :
-1×15 / 30 < x/ 30 < -1× 6/ 30
⇔ -15 < x < -6
Vậy x từ { -14 ; -13; -12 ; -11 ; -10 …..; -5 }
Cho mk ctlhn nha ! <3
Đáp án:
$a) x\in \{-3,-2,-1\}\\
b) x=-7\\
c)x \in \{9,10,11\}\\
d) x\in\{-14,-13,-12,-11,-10,-9,-8,-7\}$
Giải thích các bước giải:
$a) \frac{-1}{2}<\frac{x}{8}<\frac{-7}{15}\\
\Leftrightarrow \frac{-8}{2}<\frac{8x}{8}<\frac{(-7).8}{15}\\
\Leftrightarrow -4<x<\frac{-56}{15}\\ \Leftrightarrow x\in \{-3,-2,-1\}
b) \frac{-1}{3}<\frac{x}{24}<\frac{-1}{4}\\
\Leftrightarrow \frac{24.(-1)}{3}<\frac{24x}{24}<\frac{(-1).24}{4}\\
\Leftrightarrow -8<x<-6 \Leftrightarrow x \in \{-7\}\\
c) \frac{4}{21}<\frac{x}{42}<\frac{2}{7}\\
\Leftrightarrow \frac{42.4}{21}<\frac{42x}{42}<\frac{42.2}{7}\\
\Leftrightarrow 8<x<12 \Leftrightarrow x \in \{9,10,11\}\\
d) \frac{-1}{2}<\frac{x}{30}<\frac{-1}{5}\\
\Leftrightarrow \frac{30.(-1)}{2}<\frac{30x}{30}<\frac{(-1).30}{5}\\
\Leftrightarrow -15<x<-6 \Leftrightarrow x\in\{-14,-13,-12,-11,-10,-9,-8,-7\}$