Tìm x , biết
a, /x/+3x=4
b, /x+2/+2x=16
Tìm số abcd nếu
4abcd = dcba
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a: \(\left|3x-2\right|=4\)
\(\Leftrightarrow\left[{}\begin{matrix}3x-2=4\\3x-2=-4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-\dfrac{2}{3}\end{matrix}\right.\)
b: Ta có: \(\left|5x-3\right|=\left|x-7\right|\)
\(\Leftrightarrow\left[{}\begin{matrix}5x-3=x-7\\5x-3=7-x\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}4x=-4\\6x=10\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=\dfrac{5}{3}\end{matrix}\right.\)
\(a,\text{Với }x< -2\Rightarrow3-x-x-2=4\\ \Rightarrow-2x=3\Rightarrow x=-\dfrac{3}{2}\left(ktm\right)\\ \text{Với }-2\le x< 3\Rightarrow3-x+x+2=4\\ \Rightarrow0x=-1\Rightarrow x\in\varnothing\\ \text{Với }x\ge3\Rightarrow x-3+x+2=4\\ \Rightarrow2x=5\Rightarrow x=\dfrac{5}{2}\left(ktm\right)\)
Vậy \(x\in\varnothing\)
\(b,\text{Với }x< 2\Rightarrow4-2x+18-6x=21\\ \Rightarrow22-8x=21\Rightarrow x=\dfrac{1}{8}\left(tm\right)\\ \text{Với }2\le x< 3\Rightarrow2x-4+18-6x=21\\ \Rightarrow-4x+14=21\Rightarrow x=-\dfrac{7}{4}\left(ktm\right)\\ \text{Với }x\ge3\Rightarrow2x-4+6x-18=21\\ \Rightarrow8x=43\Rightarrow x=\dfrac{43}{8}\left(tm\right)\)
Vậy \(x\in\left\{\dfrac{1}{8};\dfrac{43}{8}\right\}\)
Bài 1:
a) Ta có: \(\dfrac{17}{6}-x\left(x-\dfrac{7}{6}\right)=\dfrac{7}{4}\)
\(\Leftrightarrow\dfrac{17}{6}-x^2+\dfrac{7}{6}x-\dfrac{7}{4}=0\)
\(\Leftrightarrow-x^2+\dfrac{7}{6}x+\dfrac{13}{12}=0\)
\(\Leftrightarrow-12x^2+14x+13=0\)
\(\Delta=14^2-4\cdot\left(-12\right)\cdot13=196+624=820\)
Vì Δ>0 nên phương trình có hai nghiệm phân biệt là:
\(\left\{{}\begin{matrix}x_1=\dfrac{14-2\sqrt{205}}{-24}=\dfrac{-7+\sqrt{205}}{12}\\x_2=\dfrac{14+2\sqrt{2015}}{-24}=\dfrac{-7-\sqrt{205}}{12}\end{matrix}\right.\)
b) Ta có: \(\dfrac{3}{35}-\left(\dfrac{3}{5}-x\right)=\dfrac{2}{7}\)
\(\Leftrightarrow\dfrac{3}{5}-x=\dfrac{3}{35}-\dfrac{10}{35}=\dfrac{-7}{35}=\dfrac{-1}{5}\)
hay \(x=\dfrac{3}{5}-\dfrac{-1}{5}=\dfrac{3}{5}+\dfrac{1}{5}=\dfrac{4}{5}\)
`2x-15 = 17``
`=> 2x = 17 + 15`
`=> 2x = 32`
`=> X = 32 : 2`
`=> x = 16`
`156 - (x + 61) = 82`
`=> x + 61 = 156 - 82`
`=> x + 61 = 74`
`=> x = 13`
`2x - 138 = 2^3 . 3^2`
`=>2x - 138 = 72`
`=> 2x = 210`
`=> x = 105`
bài 2:
`23-3x = 8`
`=> 3x = 23 - 8`
`=> 3x = 15`
`=> x = 5`
`(x-35) - 120 = 0`
`=>(x-35) = 120`
`=> x = 120 +35`
`=> x = 155`
`3^x + 2 = 29`
`=> 3^x = 27`
`=> 3^x = 3^3`
`=> x = 3`
a: -2x(x+3)+x(2x-1)=10
=>-2x^2-6x+2x^2-x=10
=>-7x=10
=>x=-10/7
b: Sửa đề: 2/3x(9/2x+1/4)-(3x^2+2)=3
=>3x^2+1/6x-3x^2-2=3
=>1/6x-2=3
=>x=30
a.\(2^x-2^4.2^7.32=0\)
\(2^x-2^{16}=0\)
\(=>x=16\)
b.\(3^x+3^{x+2}=270\)
\(3^x+3^x.3^2=270\)
\(3^x.10=270\)
\(3^x=27\)
\(=>x=3\)
b: =>4x^2+8x-8x^2+5x-10=0
=>-4x^2+13x-10=0
=>x=2 hoặc x=5/4
c: =>2x^2-5x+6x-15=2x^2+8x
=>x-15=8x
=>-7x=15
=>x=-15/7
d: =>3x^2+15x-2x-10-3x^2-12x=5
=>x-10=5
=>x=15
e: =>x^2-3x+2x^2+2x=3x^2-12
=>-x=-12
=>x=12
a, \(\left|x\right|+3x=4\left(1\right)\)
\(\left(+\right)x\ge0=>\) (1) trở thành: \(x+3x=4=>4x=4=>x=1\)
\(\left(+\right)x< 0=>\)(1) trở thành : \(-x+3x=4=>2x=4=>x=2\)
b,tương tự ,xét 2 TH \(x\ge-2;x< -2\)