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a) \(4x^2-12x=-9\)
\(\Leftrightarrow4x^2-12x+9=0\)
\(\Leftrightarrow\left(2x-3\right)^2=0\)
\(\Leftrightarrow2x-3=0\Leftrightarrow x=\frac{3}{2}\)
b) \(\left(5-2x\right)\left(2x+7\right)=4x^2-25\)
\(\Leftrightarrow\left(5-2x\right)\left(2x+7\right)+\left(25-4x^2\right)=0\)
\(\Leftrightarrow\left(5-2x\right)\left(2x+7\right)+\left(5-2x\right)\left(5+2x\right)=0\)
\(\Leftrightarrow\left(5-2x\right)\left(2x+7+5+2x\right)=0\)
\(\Leftrightarrow\left(5-2x\right)\left(4x+12\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x=\frac{5}{2}\\x=-3\end{array}\right.\)
c)\(x^3+27+\left(x+3\right)\left(x-9\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(x^2-3x+9\right)+\left(x+3\right)\left(x-9\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(x^2-3x+9+x-9\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(x^2-2x\right)=0\)
\(\Leftrightarrow\left(x+3\right)x\left(x-2\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x=-3\\x=0\\x=2\end{array}\right.\)
d) \(4\left(2x+7\right)^2-9\left(x+3\right)^2=0\)
\(\Leftrightarrow\left[2\left(2x+7\right)-3\left(x+3\right)\right]\left[2\left(2x+7\right)+3\left(x+3\right)\right]=0\)
\(\Leftrightarrow\left(4x+14-3x-9\right)\left(4x+14+3x+9\right)=0\)
\(\Leftrightarrow\left(x+5\right)\left(7x+23\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x=-5\\x=-\frac{23}{17}\end{array}\right.\)
a) \(4x^2-8x=0\)
\(\Rightarrow4x\left(x-2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}4x=0\\x-2=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=0+2\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\x=2\end{matrix}\right.\)
Vậy \(x_1=0;x_2=2\)
b) \(\left(x+5\right)-3x\left(x+5\right)=0\)
\(\Rightarrow-3x^2-14x+5=0\)
\(\Leftrightarrow\left(-3x+1\right)\left(x+5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}-3x+1=0\\x+5=0\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=\dfrac{1}{3}\\x=-5\end{matrix}\right.\)
Vậy \(x_1=-5;x_2=\dfrac{1}{3}\)
\(a,4x^2-8x=0\Rightarrow4x\left(x-8\right)=0\Rightarrow\left[{}\begin{matrix}4x=0\\x-8=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=8\end{matrix}\right.\)\(b,\left(x+5\right)-3x\left(x+5\right)=0\Leftrightarrow\left(x+5\right)\left(1-3x\right)=0\Rightarrow\left[{}\begin{matrix}x+5=0\\1-3x=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-5\\3x=1\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-5\\x=\dfrac{1}{3}\end{matrix}\right.\)
a)
x (x - 1) + x - 1 = 0
x2 - x + x - 1 = 0
x2 - 1 = 0
x2 = 1
\(\Rightarrow\) x = \(\pm\)1
b)
3( x - 3) - 4x - 12 = 0
3x - 9 - 4x - 12 = 0
-x - 21 = 0
-x = 21
\(\Rightarrow\)x = -21
c)
x3 - 5x = 0
x( x2 - 5) = 0
\(\Leftrightarrow\left\{{}\begin{matrix}x=0\\x2-5=0\Rightarrow x2=5\Rightarrow x\in\varnothing\end{matrix}\right.\)
\(\Rightarrow\)x = 0
d)
(3x - 2)2 - (x + 2)2 = 0
9x2 - 12x + 4 - x2 - 4x - 4 = 0
8x2 - 16x = 0
(làm tương tự như c)
e)
x2 - 9 - 4(x + 3) = 0
x2 - 9 - 4x - 12 = 0
(x2 - 4x + 4) - 13 -12 = 0
(x - 2)2 - 25 = 0
(x - 2)2 = 25
\(\Rightarrow\) x - 2 = 5
\(\Rightarrow\)x = 7
a ) \(\left(5x+7\right)\left(x-7\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{7}{5}\\x=7\end{matrix}\right.\)
b ) \(\left(x^2-1\right)\left(x+3\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(x+3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-1\\x=-3\end{matrix}\right.\)
c )\(x^2-x-6=0\)
\(\Leftrightarrow x^2-3x+2x-6=0\)
\(\Leftrightarrow\left(x+2\right)\left(x-3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=3\end{matrix}\right.\)
d ) \(x^2+x-12=0\)
\(\Leftrightarrow x^2-4x+3x-12\)
\(\Leftrightarrow\left(x+3\right)\left(x-4\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=4\end{matrix}\right.\)
e ) \(15\left(x+9\right)\left(x-3\right)\left(x+21\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-9\\x=3\\x=-21\end{matrix}\right.\)
g ) \(\left(x^2+1\right)\left(x^2+4x+4\right)=0\)
\(\Leftrightarrow\left(x^2+1\right)\left(x+2\right)^2=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x^2=-1\left(loại\right)\\x=-2\end{matrix}\right.\)
i ) \(x^4+2x^3-2x^2+2x-3=0\)
\(\Leftrightarrow x^4+3x^3-x^3-3x^2+x^2+3x-x-3=0\)
\(\Leftrightarrow x^3\left(x+3\right)-x^2\left(x+3\right)+x\left(x+3\right)-\left(x+3\right)=0\)
\(\Leftrightarrow\left(x^3-x^2+x-1\right)\left(x+3\right)=0\)
\(\Leftrightarrow\left(x^2+1\right)\left(x-1\right)\left(x+3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x^2=-1\left(loại\right)\\x=1\\x=-3\end{matrix}\right.\)
h) \(x^2+5x+6=0\)
\(\Leftrightarrow x^2+3x+2x+6=0\)
\(\Leftrightarrow\left(x+2\right)\left(x+3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=-3\end{matrix}\right.\)
b) \(7x\left(x-2\right)-\left(x-2\right)=0\)
<=> \(\left(7x-1\right)\left(x-2\right)=0\)
=> x=1/7 hoặc x=2
c) <=> (2x-1)3 =0
=> x=1/2
d)<=> \(\left(2x-3\right)\left(2x+3\right)-x\left(2x-3\right)=0\)
<=> \(\left(2x-3\right)\left(x+3\right)=0\)
=> x=3/2 hoặc x=-3
e) <=>\(x^2\left(x+5\right)+9\left(x+5\right)=0\)
<=> \(\left(x+5\right)\left(x^2+9\right)=0\)
=> x=-5
f) \(x^3-6x^2-x+30=0\)
<=>\(x^3+2x^2-8x^2-16x+15x+30=0\)
<=>\(x^2\left(x+2\right)-8x\left(x+2\right)+15\left(x+2\right)=0\)
<=>\(\left(x+2\right)\left(x^2-5x-3x+15\right)=0\)
<=> \(\left(x+2\right)\left(x-5\right)\left(x-3\right)=0\)
=> x=-2 hoặc x=5 hoặc x=3
câu a, b, c dễ mà. Bạn áp dụng 7 hằng đẳng thúc là làm đc thoii!!
vd: a) \(\left(9x^2-4\right)\left(x+1\right)=\left(3x+2\right)\left(x^2-1\right)\)
\(\Rightarrow\left(3x-2\right)\left(3x+2\right)\left(x+1\right)=\left(3x+2\right)\left(x-1\right)\left(x+1\right)\)
\(\Rightarrow\left(3x-2\right)\left(3x+2\right)-\left(3x+2\right)\left(x-1\right)\left(x+1\right)=0\)
\(\Rightarrow\left(3x+2\right)\left(x+1\right)[\left(3x-2\right)-\left(x-1\right)]=0\)
\(\Rightarrow\left(3x+2\right)\left(x+1\right)\left(2x-1\right)=0\) (bạn phá ngoặc ra rồi tính là ra bước này)
\(\Leftrightarrow3x+2=0\) hoặc \(x+1=0\) hoặc \(2x-1=0\) ( đến đây bạn chia làm 3 trường hợp r tự tính nhé)
Chúc bạn học tốt!!
d/
\(\Leftrightarrow x^3\left(x+1\right)+\left(x+1\right)=0\)
\(\Leftrightarrow\left(x^3+1\right)\left(x+1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+1=0\\x^3+1=0\end{matrix}\right.\) \(\Rightarrow x=-1\)
e/
\(\Leftrightarrow x^3+x^2-6x-x^2-x+6=0\)
\(\Leftrightarrow x\left(x^2+x-6\right)-\left(x^2+x-6\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(x^2+x-6\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(x-2\right)\left(x+3\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=1\\x=2\\x=-3\end{matrix}\right.\)
a/ Sai đề à??
\(\left(2x^3-3\right)^2-\left(4x^2-9\right)=0\)
\(\Leftrightarrow4x^6-12x^3+9-4x^2+9=0\)
\(\Leftrightarrow4x^6-13x^2-4x^2+18=0\)
b/ \(\Leftrightarrow\left(x^2-3\right)\left(x^2+3\right)+2x\left(x^2-3\right)=0\)
\(\Leftrightarrow\left(x-\sqrt{3}\right)\left(x+\sqrt{3}\right)\left(x^2+3+2x\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\sqrt{3}\\x=-\sqrt{3}\end{matrix}\right.\) (do \(x^2+3+2x>0\forall x\))
d/ \(\Leftrightarrow2\left(x+5\right)-x\left(x+5\right)=0\)
\(\Leftrightarrow\left(2-x\right)\left(x+5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-5\end{matrix}\right.\)
Câu a : Mình ko biết làm .
Câu b : Bạn làm rồi khỏi làm nữa
Câu c :
\(x\left(2x-7\right)-4x+14=0\)
\(x\left(2x-7\right)-\left(4x-14\right)=0\)
\(x\left(2x-7\right)-2\left(2x-7\right)=0\)
\(\left(2x-7\right)\left(x-2\right)=0\)
\(\left[{}\begin{matrix}2x-7=0\\x-2=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\dfrac{7}{2}\\x=2\end{matrix}\right.\)
Vậy \(x=\dfrac{7}{2}\) và \(x=2\)
Câu d :
\(\left(2x-3\right)^2-\left(x+5\right)^2=0\)
\(\left(2x-3-x-5\right)\left(2x-3+x+5\right)=0\)
\(\left(x-8\right)\left(3x+2\right)=0\)
\(\left[{}\begin{matrix}x-8=0\\3x+2=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=8\\x=-\dfrac{2}{3}\end{matrix}\right.\)
Vậy \(x=8\) và \(x=-\dfrac{2}{3}\)
Vậy em xin câu a ^^
a, \(6x^3+x^2+x+1=0\)
\(\Rightarrow6x^3+3x^2-2x^2-x+2x+1=0\)
\(\Rightarrow3x^2\left(2x+1\right)-x\left(2x+1\right)+\left(2x+1\right)=0\)
\(\Rightarrow\left(2x+1\right)\left(3x^2-x+1\right)=0\) (1)
Ta có: \(3x^2-x+1=3x^2-\dfrac{1}{2}x-\dfrac{1}{2}x+\dfrac{1}{12}+\dfrac{11}{12}\)
\(=3x\left(x-\dfrac{1}{6}\right)-\dfrac{1}{2}\left(x-\dfrac{1}{6}\right)+\dfrac{11}{12}\)
\(=3\left(x-\dfrac{1}{6}\right)^2+\dfrac{11}{12}>0\) (2)
Từ (1) và (2) suy ra \(2x+1=0\Rightarrow x=-\dfrac{1}{2}\)
Chúc bạn học tốt!!!
`@` `\text {Ans}`
`\downarrow`
`a,`
`(x - 2)(x - 3) =0`
`<=>`\(\left[{}\begin{matrix}x-2=0\\x-3=0\end{matrix}\right.\)
`<=>`\(\left[{}\begin{matrix}x=0+2\\x=0+3\end{matrix}\right.\)
`<=>`\(\left[{}\begin{matrix}x=2\\x=3\end{matrix}\right.\)
Vậy, `S = {2; 3}`
`b,`
`x^2 - 5x = 0`
`<=> x(x - 5) = 0`
`<=>`\(\left[{}\begin{matrix}x=0\\x-5=0\end{matrix}\right.\)
`<=>`\(\left[{}\begin{matrix}x=0\\x=0+5\end{matrix}\right.\)
`<=>`\(\left[{}\begin{matrix}x=0\\x=5\end{matrix}\right.\)
Vậy, `S = {0; 5}`
`c,`
`x^2 - 9 = 0`
`<=> x^2 = 0 + 9`
`<=> x^2 = 9`
`<=> x^2 = (+-3)^2`
`<=> x = +-3`
Vậy, `S = {3; -3}`
`d,`
`4x^2 - 25 = 0`
`<=> 4x^2 = 25`
`<=> x^2 = 25/4`
`<=> x^2 = (+-5/2)^2`
`<=> x = +-5/2`
Vậy,` S = {5/2; -5/2}.`
a: =>x-2=0 hoặc x-3=0
=>x=2 hoặc x=3
b: =>x(x-5)=0
=>x=0 hoặc x=5
c: =>(x-3)(x+3)=0
=>x=3 hoặc x=-3
d: =>(2x-5)(2x+5)=0
=>x=5/2 hoặc x=-5/2