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Ta có :
\(x^2-15x=0\)
\(\Leftrightarrow\)\(x\left(x-15\right)=0\)
\(\Leftrightarrow\)\(\orbr{\begin{cases}x=0\\x-15=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=0\\x=15\end{cases}}}\)
Vậy \(x=0\) hoặc \(x=15\)
Chúc bạn học tốt ~
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a) -3x - 8 = -7
-3x = -7 + 8
-3x = 1
x = -1/3
b) (3 - x)(x + 7) = 0
3 - x = 0 hoặc x + 7 = 0
x = 3 hoặc x = -7
a) -3x-8=-7
<=> -3x=1
<=> x=\(-\frac{1}{3}\)
Vậy x=\(-\frac{1}{3}\)
b) (3-x)(x+7)=0
<=> 3-x=0 hoặc x+7=0
<=> x=3 hoặc x=-7
Vậy x=3; x=-7
![](https://rs.olm.vn/images/avt/0.png?1311)
`4.(x+5)^3-7=101`
`4.(x+5)^3=108`
`(x+5)^3=27`
`(x+5)^3=3^3 `
`x+5=3`
`x=-2`
![](https://rs.olm.vn/images/avt/0.png?1311)
a, nhân xét / x+2/ >= 0 với mọi x
dấu bằng xảy ra khi và chỉ khi
x+ 2= 0
=> x= -2
b, / x-5/ = /-7/
=> /x-5/= 7
xét 2 TH
TH1 / x-5/ = x-5
=> x-5 = 7
=> x= 12
TH2 / x-5/ = -(x-5) = -x+5 = 5-x
=> 5-x=7
=> x= -2
![](https://rs.olm.vn/images/avt/0.png?1311)
Dùng công thức tính tổng
\(1+2+3+...+x=11325\)
\(\Leftrightarrow\frac{x\left(x+1\right)}{2}=11325\)
\(\Leftrightarrow x\left(x+1\right)=22650\)
\(\Leftrightarrow x\left(x+1\right)=150.151\)
Nên x = 150
Vậy ,,,
\(1+2+3+4+...+x=11325\)
\(\Rightarrow\frac{x\left(x+1\right)}{2}=11325\)
\(\Rightarrow x\left(x+1\right)=11325\times2\)
\(\Rightarrow x\left(x+1\right)=22650\)
\(\Rightarrow150\times151=22650\)
\(\Rightarrow x=150\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a, Ta có : \(14⋮2x-3\)
\(\Rightarrow2x-3\inƯ\left(14\right)=\left\{\pm1;\pm2;\pm7;\pm14\right\}\)
Vì \(2x-3\)là số lẻ
\(\Rightarrow2x-3\in\left\{\pm1;\pm7\right\}\)
... (tự làm)
\(b,\left(x-3\right)\left(y+2\right)=-7\)
\(x+3\)và \(y+2\)là số nguyên
\(\Rightarrow x+3,y+2\inƯ\left(-7\right)=\left\{\pm1;\pm7;\right\}\)
...
\(c,x\left(y-1\right)=9\)
\(x\)và \(y-1\)là số lẻ
\(\Rightarrow x,y-1\inƯ\left(9\right)=\left\{\pm1;\pm3;\pm9\right\}\)
...
![](https://rs.olm.vn/images/avt/0.png?1311)
1, Ta có :
\(x+\frac{3}{5}=\frac{4}{7}\div\frac{8}{21}\)
\(x+\frac{3}{5}=\frac{4}{7}\times\frac{21}{8}\)
\(x+\frac{3}{5}=\frac{3}{2}\)
\(x=\frac{3}{2}-\frac{3}{5}\)
\(x=\frac{15}{10}-\frac{6}{10}\)
\(x=\frac{9}{10}\)
Vậy x = \(\frac{9}{10}\)
2, Ta có :
\(\frac{2}{3}+\frac{3}{4}\div x=-\frac{1}{6}\)
\(\frac{3}{4}\div x=-\frac{1}{6}-\frac{2}{3}\)
\(\frac{3}{4}\div x=-\frac{1}{6}-\frac{4}{6}\)
\(\frac{3}{4}\div x=-\frac{5}{6}\)
\(x=\frac{3}{4}\div\left(-\frac{5}{6}\right)\)
\(x=\frac{3}{4}\times\left(-\frac{6}{5}\right)\)
\(x=-\frac{9}{10}\)
Vậy x = \(-\frac{9}{10}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(450:\left(x-19\right)=50\\ \Leftrightarrow x-19=5\\ \Leftrightarrow x=24\)
\(2\left(x-52\right)=2.23+20\\ \Leftrightarrow2\left(x-52\right)=66\\ \Leftrightarrow x-52=33\\ \Leftrightarrow x=85\)
\(10-\left(x-3\right):2=72-100\\ \Leftrightarrow10-\left(x-3\right):2=-28\\ \Leftrightarrow10-\left(x-3\right)=-56\\ \Leftrightarrow x-3=66\\ \Leftrightarrow x=69\)
1.x-19=450:50
x-19=9
x =9+19
x =28
2. 2(x-51)=46+20
2(x-51)=66
x-51=66:2
x-51=33
x =33+51
x =84
\(4\times\left(x+5\right)^3-7=101\)
\(\Rightarrow4\times\left(x+5\right)^3=101+7\)
\(\Rightarrow4\times\left(x+5\right)^3=108\)
\(\Rightarrow\left(x+5\right)^3=108\div4\)
\(\Rightarrow\left(x+5\right)^3=27\)
\(\Rightarrow\left(x+5\right)^3=3^3\)
\(\Rightarrow x+5=3\)
\(\Rightarrow x=3-5\)
\(\Rightarrow x=-2\)
Keuka
4(x+5)3-7=101
4(x+5)3=101+7
4(x+5)3=108
(x+5)3=108:4
(x+5)3=27
(x+5)3=33
=> x+5=3
x=3-5
x=-2
Vậy x=-2