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* \(20+65.4=\left(x+75\right):5+30\)
\(\Leftrightarrow20+260-30=\frac{x}{5}+\frac{75}{5}\)
\(\Leftrightarrow20+260-30-\frac{75}{5}=\frac{x}{5}\)
\(\Leftrightarrow235=\frac{x}{5}\Rightarrow x=235.5=1175\)
* \(2248:\left[119-\left(x-6\right)\right]=24\)
\(\Leftrightarrow2248:\left(119-x+6\right)=24\)
\(\Leftrightarrow2248:\left(125-x\right)=24\)
A mình lỡ tay, để mình tính tiếp nhá!
\(\Leftrightarrow125-x=2248:24\Leftrightarrow125-x=\frac{281}{3}\Rightarrow-x=\frac{94}{3}\Rightarrow x=-\frac{94}{3}\)(bài này mình thấy sai sai sao á, nếu mình làm sai thì thông cảm cho mình nhé!
* \(\left(x+70\right):14-40=\left(32.15\right):2\)
\(\Leftrightarrow\left(x+70\right):14=480:2+40\)
\(\Leftrightarrow\frac{x}{14}+5=280\Leftrightarrow\frac{x}{14}=275\Rightarrow x=3850\)
* \(x-4867=\left(175.2050.70\right):25+23\)
\(\Leftrightarrow x-4867-23=\left(175:25\right).\left(2050:25\right).\left(70:25\right)\)
\(\Leftrightarrow x-4890=7.82.\frac{14}{5}\)
\(\Leftrightarrow x-4890=\frac{8036}{5}\Rightarrow x=\frac{8036}{5}+4890=\frac{32486}{5}\)(bài này mình thấy hình như cũng có cái gì đó sai sai luôn hihi!)
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các bạn làm theo cách lớp 6 cho minh nha nếu các bạn có câu hỏi mà mình làm đc mình sẽ giúp
a) -12 . (x - 5) + 7 . (3 - x) = 5
=> -12x + 60 + 21 - 7x = 5
=> -12x - 7x = 5 - 60 - 21
=> -19x = -76
=> x = -76 : (-19)
=> x = 4
b) 30 . (x + 2 ) - 6 . (x - 5) - 24 . x = 100
=> 30x + 60 - 6x + 30 - 24x = 100
=> 30x - 6x - 24x = 100 - 30 - 60
=> x . (30 - 6 - 24) = 70 - 60
=> x . 0 = 10 (Vô lí vì ko có số nào . 0 = 10)
=> x thuộc rỗng
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`@` `\text {Ans}`
`\downarrow`
`[ (100 - x)*2 - 2] = 40`
`=> (100-x)*2 - 2 = 40`
`=> (100 - x)*2 = 40 + 2`
`=> (100 - x)*2 = 42`
`=> 100 - x = 42 \div 2`
`=> 100 - x = 21`
`=> x = 100 - 21`
`=> x = 79`
Vậy, `x=79.`
\(\left[\left(100-x\right).2-2\right]=40\)
\(=>\left(100-x\right).2=40+2\)
\(=>\left(100-x\right).2=42\)
\(=>100-x=42:2\)
\(=>100-x=21\)
\(=>x=100-21\)
\(=>x=79\)
Chúc bạn học tốt
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a) -12.(x - 5) + 7(3 - x) = 5
=> -12x + 60 + 21 - 7x = 5
=> -19x + 81 = 5
=> -19x = 5 - 81
=> -19x = -76
=> x = -76 : (-19)
=> x = 4
b) (x + 1) + (x + 2) + (x + 3) + ... + (x + 20) = 250
=> (x + x + x + ... + x) + (1 + 2 + 3 + ... + 20) = 250
=> 20x + 210 = 250
=> 20x = 250 - 210
=> 20x = 40
= > x = 40 : 20
=> x = 2
\(-12\left(x-5\right)+7\left(3-x\right)=5\)
\(\Leftrightarrow-12x+60+21-7x=5\)
\(\Leftrightarrow-19x+81=5\)
\(\Leftrightarrow81-5=19x\)
\(\Leftrightarrow19x=76\)
\(\Leftrightarrow x=4\)
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=> x + 4 = 0 => x = -4
hoặc 23 - x =0 => x = 23
Vậy x = -4 ; x = 23
=> x+4 = 0 hoặc 23-x = 0
x = 0-4 hoặc x = 23-0
x = 4 hoặc x = 23
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7.( x-6 )= 4x +9
=> 7x - 42 - 4x = 9
=> 3x = 51
=> x = 17
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Ta có \(\dfrac{2}{1\cdot5}+\dfrac{2}{5\cdot9}+\dfrac{2}{9\cdot13}+...+\dfrac{2}{x\left(x+4\right)}=\dfrac{56}{113}\)
\(\dfrac{1}{2}\left(\dfrac{4}{1\cdot5}+\dfrac{4}{5\cdot9}+\dfrac{4}{9\cdot13}+...+\dfrac{4}{x\left(x+4\right)}\right)=\dfrac{56}{113}\)
\(1-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{13}+...+\dfrac{1}{x}-\dfrac{1}{x+4}=\dfrac{56}{113}:\dfrac{1}{2}\)
\(1-\dfrac{1}{x+4}=\dfrac{112}{113}\)
\(\dfrac{1}{x+4}=1-\dfrac{112}{113}=\dfrac{1}{113}\)
x + 4 = 113 ⇒ x = 109
\(\dfrac{2}{1.5}+\dfrac{2}{5.9}+...+\dfrac{2}{x\left(x+4\right)}=\dfrac{56}{113}\)
Xét: \(A=\dfrac{2}{1.5}+\dfrac{2}{5.9}+...+\dfrac{2}{x\left(x+4\right)}\)
\(A=\dfrac{1}{2}.\left(1-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{9}+...+\dfrac{1}{x-4}-\dfrac{1}{x}+\dfrac{1}{x}-\dfrac{1}{x+4}\right)\)
\(A=\dfrac{1}{2}.\left(1-\dfrac{1}{x+4}\right)\)
Với \(A=\dfrac{56}{113}\) thì
\(\dfrac{1}{2}.\left(1-\dfrac{1}{x+4}\right)=\dfrac{56}{113}\)
\(\left(1-\dfrac{1}{x+4}\right)=\dfrac{112}{113}\)
\(\dfrac{1}{x+4}=\dfrac{1}{113}\)
\(x=109\)
x+30%.x=1.3
x+(x.30)/100 =1,3
(100x+30x)/100=1,3
130x=130
x=1
\(x+30\%.x=1,3\)
\(\Rightarrow x+\frac{3}{10}.x=1,3\)
\(\Rightarrow x\left(1+\frac{3}{10}\right)=1,3\)
\(\Rightarrow x.\frac{13}{10}=1,3\)
\(\Rightarrow x=1\)