Tìm x biết rằng:
a)25x^2-9=0
b)8x^3-50x=0
K
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TT
2
29 tháng 10 2020
8x3 - 50x = 0
⇔ 2x( 4x2 - 25 ) = 0
⇔ 2x( 2x - 5 )( 2x + 5 ) = 0
⇔ 2x = 0 hoặc 2x - 5 = 0 hoặc 2x + 5 = 0
⇔ x = 0 hoặc x = ±5/2
( x + 3 )2 = 9( 2x - 1 )2
⇔ ( x + 3 )2 - 32( 2x - 1 )2 = 0
⇔ ( x + 3 )2 - [ 3( 2x - 1 ) ]2 = 0
⇔ ( x + 3 )2 - ( 6x - 3 )2 = 0
⇔ ( x + 3 - 6x + 3 )( x + 3 + 6x - 3 ) = 0
⇔ ( -5x + 6 ).7x = 0
⇔ -5x + 6 = 0 hoặc 7x = 0
⇔ x = 6/5 hoặc x = 0
29 tháng 10 2020
\(8x^3-50x=0\)
\(2x\left(4x^2-25\right)=0\)
\(\orbr{\begin{cases}2x=0\\4x^2-25=0\end{cases}}\)
\(\orbr{\begin{cases}x=0\\x^2=\frac{25}{4}\end{cases}}\)
\(\orbr{\begin{cases}x=0\\x=\pm\sqrt{\frac{25}{4}}\end{cases}}\)
\(\orbr{\begin{cases}x=0\\x=\pm\frac{5}{2}\end{cases}}\)
\(\left(x+3\right)^2=9\left(2x-1\right)^2\)
\(x^2+6x+9=9\left(4x^2-4x+1\right)\)
\(x^2+6x+9=36x^2-36x+9\)
\(0=36x^2-36x+9-x^2-6x-9\)
\(0=35x^2-42x\)
\(35x^2-42x=0\)
\(7x\left(5x-6\right)=0\)
\(\orbr{\begin{cases}7x=0\\5x-6=0\end{cases}}\)
\(\orbr{\begin{cases}x=0\\x=\frac{6}{5}\end{cases}}\)
DT
4
NN
8 tháng 12 2019
\(2x\left(x^2-25\right)=0\)
\(\Rightarrow\orbr{\begin{cases}2x=0\\x^2-25=0\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=0\\x=\pm5\end{cases}}\)
\(2x\left(3x-5\right)+\left(3x-5\right)=0\)
\(\left(2x+1\right)\left(3x-5\right)=0\)
\(\Rightarrow\orbr{\begin{cases}2x+1=0\\3x-5=0\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=-\frac{1}{2}\\x=\frac{5}{3}\end{cases}}\)
NN
8 tháng 12 2019
\(9\left(3x-2\right)-x\left(2-3x\right)=0\)
\(9\left(3x-2\right)+x\left(3x-2\right)=0\)
\(\left(9+x\right)\left(3x-2\right)=0\)
\(\Rightarrow\orbr{\begin{cases}9+x=0\\3x-2=0\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=-9\\x=\frac{2}{3}\end{cases}}\)
\(\left(2x-1\right)^2=25\)
\(\Rightarrow\orbr{\begin{cases}2x-1=5\\2x-1=-5\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=3\\x=-2\end{cases}}\)
K
2
1 tháng 8 2017
a, \(2\left(x+3\right)-x^2-3x=0\)
\(\Leftrightarrow2\left(x+3\right)-x\left(x+3\right)=0\)
\(\Leftrightarrow\left(2-x\right)\left(x+3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}2-x=0\\x+3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-3\end{matrix}\right.\)
Vậy x = 2 hoặc x = -3
b, \(8x^3-50x=0\)
\(\Leftrightarrow2x\left(4x^2-25\right)=0\)
\(\Leftrightarrow2x\left(2x-5\right)\left(2x+5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}2x=0\\2x-5=0\\2x+5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{5}{2}\\x=\dfrac{-5}{2}\end{matrix}\right.\)
Vậy...
N
1 tháng 8 2017
1.
a) \(2\left(x+3\right)-x^2-3x=0\)
\(2\left(x+3\right)-\left(x^2+3x\right)=0\)
\(2\left(x+3\right)-x\left(x+3\right)=0\)
\(\left(2-x\right)\left(x+3\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}2-x=0\\x+3=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=2\\x=-3\end{matrix}\right.\)
Vậy x=2 hoặc x=-3
b) \(8x^3-50x=0\)
\(x\left(8x^2-50\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\8x^2-50=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x^2=\dfrac{25}{4}=\left(\pm\dfrac{5}{2}\right)^2\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{5}{2}\\x=\dfrac{-5}{2}\end{matrix}\right.\)
Vậy \(x=0\) hoặc \(x=\dfrac{-5}{2}\) hoặc \(x=\dfrac{5}{2}\)
tik mik nhé !!!
30 tháng 9 2016
a) \(\left(2x-1\right)^2-25=0\)
\(\left(2x-1\right)^2=0+25=25\)
\(\left(2x-1\right)^2=5^2=\left(-5\right)^2\)
\(\Rightarrow\left[\begin{array}{nghiempt}2x-1=5\\2x-1=-5\end{array}\right.\Rightarrow\left[\begin{array}{nghiempt}2x=6\\2x=-4\end{array}\right.\Rightarrow\left[\begin{array}{nghiempt}x=3\\x=-2\end{array}\right.\)
b) \(8x^3-50x=0\)
\(2x\left(4x^2-25\right)=0\)
\(\Rightarrow\left[\begin{array}{nghiempt}2x=0\\4x^2-25=0\end{array}\right.\Rightarrow\left[\begin{array}{nghiempt}x=0\\4x^2=25\Rightarrow x^2=\frac{25}{4}\Rightarrow\left[\begin{array}{nghiempt}x=\frac{5}{2}\\x=-\frac{5}{2}\end{array}\right.\end{array}\right.\)
VR
0
\(a,25x^2-9=0\)
\(\Leftrightarrow\left(5x-3\right)\left(5x+3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}5x+3=0\\5x-3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{3}{5}\\x=\dfrac{3}{5}\end{matrix}\right.\)
\(b,8x^3-50x=0\)
\(\Leftrightarrow2x\left(4x^2-25\right)=0\)
\(\Leftrightarrow2x\left(2x-5\right)\left(2x+5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\2x-5=0\\2x+5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{5}{2}\\x=-\dfrac{5}{2}\end{matrix}\right.\)