71+65x4=x+140/x+260
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Trả lời:
71+65.4=x+140/x+260
x+140/x+260=71+65.4
x+140/x+260=71+260
x+140/x=71
x/x+140/x=71
1+140/x=71
140/x=71-1
140/x=70
x=140/70
x=2
vậy x=2
cậu ơi cái chỗ 71+65x4 là nhân 4 hay là 65 nhân x nhân 4 ạ
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
71 + 65 x 4 = \(\frac{x+140}{x+260}\)
71 + 260 = \(\frac{x+140}{x+260}\)
331 = \(\frac{x+140}{x+260}\)
\(\Rightarrow x+140=331\left(x+260\right)\)
\(\Rightarrow x+140=331x+86060\)
\(\Rightarrow140-86060=331x-x\)
\(\Rightarrow330x=85920\)
\(\Rightarrow x=\frac{2864}{11}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(71+65\times4=\frac{x+140}{x}+260\)
\(71+260=\frac{x}{x}+\frac{140}{x}+260\)
\(71\) \(=1+\frac{140}{x}\)
\(70\) \(=\frac{140}{x}\)
\(x\) \(=2\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{x+140}{x+260}=71+65.4\)
\(\Leftrightarrow\frac{x+140}{x+260}=71+260\)
\(\Leftrightarrow\frac{x+140}{x+260}=331\)
\(\Leftrightarrow x+140=\left(x+260\right)331\)
\(\Leftrightarrow x+140=86060+331x\)
\(\Leftrightarrow x-331x=85920\)
\(\Leftrightarrow x\left(331-1\right)=85920\)
\(\Leftrightarrow x330=85920\)
\(\Leftrightarrow x\approx260,2\)
![](https://rs.olm.vn/images/avt/0.png?1311)
(x+1)+(x+4)+(x+7)+....+(x+28)=155
x+x+x+...+x+(1+4+7+....+28) = 155
10x + 145 = 155
=> 10x = 155 - 145
=> 10x = 10
=> x = 10:10
=> x =1
a) (x + 1 ) + ( x + 4 ) + ( x + 7 ) + ... + ( x + 28 ) = 155
( x + x + x + ... + x ) + ( 1 + 4 + 7 + ... + 28 ) = 155
10x + 145 = 145
10x = 155 - 145
10x = 10
=> x = 10 : 10
=> x = 1
71 + 65 x 4 = x + 140/x + 260
x + 140/x + 260 = 71 + 65 x 4
x + 140/x + 260 = 71 + 260
x + 140/x = 71
x/x + 140/x = 71
1 + 140/x = 71
140/x = 71 - 1
140/x = 70
x = 140/70
x = 2
ích=2
nhớ nha !