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\(x^3-9x^2+27x-27=-8\Leftrightarrow\left(x^3-27\right)-\left(9x^2-27x\right)=\left(x-3\right)\left(x^2+3x+9\right)-9x\left(x-3\right)=\left(x-3\right)\left(x^2-6x+9\right)=\left(x-3\right)^3=-8=\left(-2\right)^3\Rightarrow x=\left(-2\right)+3=1\)
\(64x^3+48x^2+12x+1=\left(64x^3+1\right)+\left(48x^2+12x\right)=\left(4x+1\right)\left(16x^2-4x+1\right)+12x\left(4x+1\right)=\left(4x+1\right)\left(16x^2+8x+1\right)=\left(4x+1\right)^3=27\Rightarrow4x=2\Leftrightarrow x=\frac{1}{2}\)
c) \(\left(2x-1\right)^3-4x^2.\left(2x-3\right)=5\)
\(\Leftrightarrow\left(8x^3-12x^2+6x-1\right)-\left(8x^3-12x^2\right)=5\)
\(\Leftrightarrow8x^3-12x^2+6x-1-8x^3+12x^2=5\)
\(\Leftrightarrow6x-1=5\)
\(\Leftrightarrow6x=6\)
\(\Leftrightarrow x=1\)
d) \(\left(x+4\right)^3-x^2.\left(x+12\right)=16\)
\(\Leftrightarrow\left(x^3+12x^2+48x+64\right)-\left(x^3+12x^2\right)=16\)
\(\Leftrightarrow x^3+12x^2+48x+64-x^3-12x^2=16\)
\(\Leftrightarrow48x+64=16\)
\(\Leftrightarrow48x=-48\)
\(\Leftrightarrow x=-1\)
#vì câu a,b có người làm rồi nên mình chỉ làm c,d thôi nhé ! :)
Học Tốt !!
Bài 1:
a) \(9\left(4x+3\right)^2=16\left(3x-5\right)^2\)
\(114x^2+216x+81=114x^2-480x+400\)
\(144x^2+216x=144x^2-480x+400-81\)
\(114x^2+216=114x^2-480x+319\)
\(696x=319\)
\(\Rightarrow x=\frac{11}{24}\)
b) \(\left(x^3-x^2\right)^2-4x^2+8x-4=0\)
\(\left(x-1\right)^2\left(x^2+2\right)\left(x+\sqrt{2}\right)\left(x-\sqrt{2}\right)=0\)
\(\Rightarrow x=1\)
c) \(x^5+x^4+x^3+x^2+x+1=0\)
\(\left(x+1\right)\left(x^2+x+1\right)\left(x^2-x+1\right)=0\)
\(\Rightarrow x=-1\)
Bài 2:
a) \(5x^3-7x^2-15x+21=0\)
\(\left(5x-7\right)\left(x+\sqrt{3}\right)\left(x-\sqrt{3}\right)=0\)
\(\Rightarrow x=\frac{7}{5}\)
b) \(\left(x-3\right)^2=4x^2-20x+25\)
\(x^2-6x+9-25=4x^2-20x+25\)
\(x^2-6x+9=4x^2-20x+25-25\)
\(x^2-6x-16=4x^2-20x\)
\(x^2+14x-16=4x^2-4x^2\)
\(-3x^2+14x-16=0\)
\(\Rightarrow\orbr{\begin{cases}x=2\\x=\frac{8}{3}\end{cases}}\)
c) \(\left(x-1\right)^2-5=\left(x+2\right)\left(x-2\right)-x\left(x-1\right)\)
\(x^2-2x=x-4\)
\(x^2-2x=x-4+4\)
\(x^2-2x=x-x\)
\(x^2-3x=0\)
\(\Rightarrow\orbr{\begin{cases}x=0\\x=3\end{cases}}\)
d) \(\left(2x-3\right)^3-\left(2x+3\right)\left(4x^2-1\right)=-24\)
\(-48x^2+56x-24=-24\)
\(-48x^2+56x=-24+24\)
\(-48x^2+56=0\)
\(\Rightarrow\orbr{\begin{cases}x=0\\x=\frac{7}{6}\end{cases}}\)
mình ko chắc
a) x3 - 9x2 + 27x - 27 = -8
<=> x3 - 3x2.3 + 3x.32 - 33 = -8
<=> (x - 3)3 = -23
<=> x - 3 = -2
<=> x = 1 (T/m)
Vậy x = 1.
b) 64x3 + 48x2 + 12x + 1 = 27
<=> (4x)3 + 3.(4x)2.1 + 3.4x.12 + 13 = 27
<=> (4x + 1)3 = 33
<=> 4x + 1 = 3
<=> 4x = 2
<=> x = \(\frac{1}{2}\)(T/m)
Vậy x = \(\frac{1}{2}\).
a) \(3x^3-6x^2=0\)
\(3x^2\left(x-2\right)=0\)
\(\orbr{\begin{cases}3x^2=0\\x-2=0\end{cases}}\)
\(\orbr{\begin{cases}x=0\\x=2\end{cases}}\)
b) \(x\left(x-4\right)-12x+48=0\)
\(x^2-4x-12x+48=0\)
\(x^2-16x+48=0\)
\(\left(x-12\right)\left(x-4\right)=0\)
\(\orbr{\begin{cases}x-12=0\\x-4=0\end{cases}}\)
\(\orbr{\begin{cases}x=12\\x=4\end{cases}}\)
c) Viết thiếu nha :v
d) \(2x\left(x-5\right)-x\left(2x+3\right)=16\)
\(2x^2-10x-x^2-2x^2-3x=16\)
\(-13x=16\)
\(x=-\frac{16}{13}\)
e) \(\left(4x^2-1\right)-\left(x-1\right)^2=-3\)
\(4x^2-1-x^2+2x-1=-3\)
\(3x^2-2+2x=-3\)
\(3x^2-2+2x+3=0\)
\(3x^2+1+2x=0\)
Vì \(3x^2+1+2x>0\)nên:
\(x\in\varnothing\)
A) 3x3 - 6x2 = 0
=> 3x2(x - 2) = 0
=> \(\orbr{\begin{cases}3x^2=0\\x-2=0\end{cases}}\)
=> \(\orbr{\begin{cases}x=0\\x=2\end{cases}}\)
b) x(x - 4) - 12x + 48 = 0
=> x(x - 4) - 12(x - 4) = 0
=> (x - 12)(x - 4) = 0
=> \(\orbr{\begin{cases}x-12=0\\x-4=0\end{cases}}\)
=> \(\orbr{\begin{cases}x=12\\x=4\end{cases}}\)
c) x(x - 4) - (x2 - 8) = x2 - 4x - x2 + 8 = 4x + 8
Bài 1 :
a, \(\left(x-3\right)^2-4=0\Leftrightarrow\left(x-3\right)^2=4\Leftrightarrow\left(x-3\right)^2=\left(\pm2\right)^2\)
TH1 : \(x-3=2\Leftrightarrow x=5\)
TH2 : \(x-3=-2\Leftrightarrow x=1\)
b, \(x^2-2x=24\Leftrightarrow x^2-2x-24=0\)
\(\Leftrightarrow\left(x-6\right)\left(x+4\right)=0\)
TH1 : \(x-6=0\Leftrightarrow x=6\)
TH2 : \(x+4=0\Leftrightarrow x=-4\)
c, \(\left(2x-1\right)^2+\left(x+3\right)^2-5\left(x+2\right)\left(x-2\right)=0\)
\(\Leftrightarrow4x^2-4x+1+x^2+6x+9-5\left(x^2-4\right)=0\)
\(\Leftrightarrow2x+30=0\Leftrightarrow x=-15\)
d, tương tự
b,x3+12x2+48x+64-x3-12x2=16
48x+64=16
12x+16=4
x=1