tìm số tự nhiên x
x 15 = x
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1. \(x⋮15\Rightarrow x\in B\left(15\right)=\left\{0;15;30;45;60;75;90;105;120;135;150;...\right\}\)
mà \(45< x< 136\)
\(\Rightarrow x\in\left\{60;75;90;105;120;135\right\}\)
2.
\(18⋮x\Rightarrow x\in U\left(18\right)=\left\{1;2;3;6;18\right\}\)
mà \(x>7\Rightarrow\Rightarrow x\in\left\{18\right\}\)
a) Ta có : \(x-1\inƯ\left(12\right)=\left\{\pm1;\pm2;\pm3;\pm4;\pm6;\pm12\right\}\)
...
b) Ta có : \(2x+1\inƯ\left(28\right)=\left\{\pm1;\pm2;\pm4;\pm7;\pm12;\pm28\right\}\)
Mà \(2x+1\)là số chẵn
\(\Rightarrow2x+1\in\left\{\pm1;\pm7\right\}\)
...
c) Ta có : \(x+15\)là bội của \(x+3\)
\(\Rightarrow x+15⋮x+3\)
\(\Rightarrow x+3+12⋮x+3\)
Vì \(x+3⋮x+3\)
\(\Rightarrow12⋮x+3\)
\(\Rightarrow x+3\inƯ\left(12\right)=\left\{\pm1;\pm2;\pm3;\pm4;\pm6;\pm12\right\}\)
...
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\(\dfrac{15}{19}\times\dfrac{38}{5}< x< \dfrac{67}{15}-\dfrac{56}{16}\\ \dfrac{5\times3\times19\times2}{19\times5}< x< \dfrac{67\times16-56\times15}{15\times16}\\ 3\times2< x< \dfrac{232}{240}\\ 6< x< \dfrac{232}{240}\) (*)
Mà : \(\dfrac{232}{240}< \dfrac{240}{240}=1\\ \)
Nên (*) là vô lí ( Do `6>232/240` )
Vậy \(x\in\varnothing\)
Ta có:
15/19 × 38/5 = 6
67/15 + 56/15 = 123/15 = 8,2
Mà 6 < X < 8,2
Vậy X = 6 hoặc X = 7
vi 1 nhan voi so nao cung = chinh no
de: x^15=x^2
nen x=1
1. \(\dfrac{x}{15}< \dfrac{4}{15}\)
<=> \(x< 4\) (x \(\ne0\))
2. \(\dfrac{5}{9}>\dfrac{x}{9}\)
<=> \(5>x\) (x \(\ne0\))
3. \(1< \dfrac{x}{8}< \dfrac{11}{8}\)
<=> \(\dfrac{8}{8}< \dfrac{x}{8}< \dfrac{11}{8}\)
<=> 8 < x < 11
<=> x \(\in\left\{9;10\right\}\)
`!`
\(x^{15}=x\\ \Rightarrow x^{15}-x=0\\ \Rightarrow x\left(x^{14}-1\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=0\\x^{14}-1=0\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=0\\x^{14}=1\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=0\\x=1\end{matrix}\right.\)
Vậy \(x\in\left\{0;1\right\}\)
x=0 hoặc x=1