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x = -1
\(\Rightarrow-1=\dfrac{7}{3}.a-1\\ \Rightarrow\dfrac{7}{3}.a-1=-1\\ \dfrac{7}{3}.a=-1+1=0\\ \Rightarrow a=0\)
x = 7
\(\Rightarrow7=\dfrac{7}{3}.a-1\\ \Rightarrow\dfrac{7}{3}.a-1=7\\ \dfrac{7}{3}.a=7+1=8\\ \Rightarrow a=8:\dfrac{7}{3}=\dfrac{8}{1}.\dfrac{3}{7}=\dfrac{24}{7}\)
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a) x = 1
⇒ 3a - 1 = 5
⇒ 3a = 6
⇒ a = 2
b) x = 5
⇒ 3a - 1 = 1
⇒ 3a = 2
⇒ a = 2/3
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a) \(\dfrac{5}{3a-1}=1\)
\(\Rightarrow3a-1=5\)
\(\Rightarrow3a=6\)
\(\Rightarrow a=\dfrac{6}{3}=2\)
b) \(\dfrac{5}{3a-1}=-5\)
\(\Rightarrow3a-1=5:\left(-5\right)=-1\)
\(\Rightarrow3a=-1+1=0\)
\(\Rightarrow a=0:3=0\)
![](https://rs.olm.vn/images/avt/0.png?1311)
+) x = -1
-1 = 7/2a - 1
-2a + 1 = 7
-2x = 7 - 1
-2x = 6
x = -3
để x = -1 thì a = -3.
+) x = 7
7 = 7/2a - 1
7(2a - 1) = 7
2a - 1 = 1
2a = 1 + 1
2a = 2
a = 1
để x = 7 thì a = 1.
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a, \(\dfrac{x}{7}\) \(\in\) Q ⇔ \(x\in z\)
b, \(\dfrac{5}{x}\) \(\in\) Q ⇔ \(x\) \(\ne\) 0; \(x\) \(\in\) Z
c, - \(\dfrac{5}{2x}\) \(\in\) Q ⇔ \(x\) \(\ne\) 0; \(x\in Z\)
a) Tập hợp số nguyên chia hết cho 7 là
\(\Rightarrow x\in A=\left\{\pm7;\pm14;\pm21;...\right\}\)
\(\Rightarrow A=\left\{x\inℕ|x=\pm7k;k\inℤ\right\}\)
Vậy để \(\dfrac{x}{7}\in Q\)
\(\Rightarrow x\in A\)
b) \(\dfrac{5}{x}\inℚ\)
\(\Rightarrow x\in\left\{\pm1;\pm5\right\}\)
c) \(-\dfrac{5}{2x}\inℚ\)
\(\Rightarrow2x\in\left\{\pm1;\pm5\right\}\)
\(\Rightarrow x\in\left\{\pm\dfrac{1}{2};\pm\dfrac{5}{2}\right\}\)
\(\Rightarrow x\in\varnothing\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(x=-1\Leftrightarrow\frac{7}{3a-1}=-1\)
\(\Leftrightarrow3a-1=-7\Leftrightarrow a=-2\)
b) \(x=7\Leftrightarrow\frac{7}{3a-1}=7\)
\(\Leftrightarrow3a-1=1\Leftrightarrow a=\frac{2}{3}\)
a) x = -1
7/3a - 1 = -1
7 = -3a + 1
7 - 1 = -3a
6 = -3a
6 : (-3) = a
-2 = a
=> a = -2
b) x = 7
7/3a - 1 = 7
7 = 7(3a - 1)
7 : 7 = 3a - 1
1 = 3a - 1
1 + 1 = 3a
2 = 3a
2/3 = a
=> a = 2/3
Giải:
Ta có: x = 1
=> \(\frac{7}{3a-1}=1\)
=> \(3a-1=7\)
=> 3a = 8
=> a = 8/3
b) Ta có: x = 7
=> \(\frac{7}{3a-1}=7\)
=> 3a - 1 = 7 : 7
=> 3a - 1 = 1
=> 3a = 2
=> a = 2/3
#)Giải :
a) \(x=\frac{7}{3a-1}\)
Theo đề : \(-1=\frac{7}{3a-1}\)
Từ đây giải ra a = - 2
b) \(x=\frac{7}{3a-1}\)
theo đề : \(7=\frac{7}{3a-1}\)
Từ đây ra a = \(\frac{2}{3}\)