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a: Ta có: \(\sqrt{4x+20}-3\sqrt{x+5}+\dfrac{4}{3}\sqrt{9x+45}=6\)
\(\Leftrightarrow2\sqrt{x+5}-3\sqrt{x+5}+4\sqrt{x+5}=6\)
\(\Leftrightarrow3\sqrt{x+5}=6\)
\(\Leftrightarrow x+5=4\)
hay x=-1
b: Ta có: \(\dfrac{1}{2}\sqrt{x-1}-\dfrac{3}{2}\sqrt{9x-9}+24\sqrt{\dfrac{x-1}{64}}=-17\)
\(\Leftrightarrow\dfrac{1}{2}\sqrt{x-1}-\dfrac{9}{2}\sqrt{x-1}+3\sqrt{x-1}=-17\)
\(\Leftrightarrow\sqrt{x-1}=17\)
\(\Leftrightarrow x-1=289\)
hay x=290
a) \(\sqrt{x^2-6x+9}=3\)
⇔ \(\sqrt{\left(x-3\right)^2}=3\)
⇔ \(\left|x-3\right|=3\)
⇔ \(\orbr{\begin{cases}x-3=3\\x-3=-3\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=6\\x=0\end{cases}}\)
b) \(\sqrt{x^2-8x+16}=x+2\)
⇔ \(\sqrt{\left(x-4\right)^2}=x+2\)
⇔ \(\left|x-4\right|=x+2\)
⇔ \(\orbr{\begin{cases}x-4=x+2\left(x\ge4\right)\\4-x=x+2\left(x< 4\right)\end{cases}\Leftrightarrow}x=1\)
c) \(\sqrt{x^2+6x+9}=3x-6\)
⇔ \(\sqrt{\left(x+3\right)^2}=3x-6\)
⇔ \(\left|x-3\right|=3x-6\)
⇔ \(\orbr{\begin{cases}x-3=3x-6\left(x\ge3\right)\\3-x=3x-6\left(x< 3\right)\end{cases}}\Leftrightarrow x=\frac{9}{4}\)
d) \(\sqrt{x^2-4x+4}-2x+5=0\)
⇔ \(\sqrt{\left(x-2\right)^2}-2x+5=0\)
⇔ \(\left|x-2\right|-2x+5=0\)
⇔ \(\orbr{\begin{cases}x-2-2x+5=0\left(x\ge2\right)\\2-x-2x+5=0\left(x< 2\right)\end{cases}}\Leftrightarrow x=3\)
\(\left(x^2-2x+6\right)\left(x^2-8x+4\right)+\left(5x+1\right)\left(x+1\right)-\left(x^2-3x-3\right)\left(x^2+x-3\right)=0\)
\(\Leftrightarrow x^8-5x^2+7x-2=0\)
\(\Leftrightarrow\left(x-2\right)\left(x^2-3x+1\right)=0\)
Xong rồi nhé
\(\left(x^2-2x+6\right)\left(x^2-8x-4\right)+\left(5x+1\right)\)\(\left(x-1\right)-\left(x^2-3x-3\right)\left(x^2+x-3\right)=\)\(0\)
\(\Leftrightarrow x^8-5x^2+7x-2=0\)
\(\Leftrightarrow\left(x-2\right)\left(x^2-3x+1\right)=0\)
~ 양 셜 김 ~
a.
ĐKXĐ: $x\geq 0$
PT $\Leftrightarrow 6\sqrt{2x}-4\sqrt{2x}+5\sqrt{2x}=21$
$\Leftrightarrow 7\sqrt{2x}=21$
$\Leftrightarrow \sqrt{2x}=3$
$\Leftrightarrow 2x=9$
$\Leftrightarrow x=\frac{9}{2}$ (tm)
b.
ĐKXĐ: $x\geq -2$
PT $\Leftrightarrow \sqrt{25(x+2)}+3\sqrt{4(x+2)}-2\sqrt{16(x+2)}=15$
$\Leftrightarrow 5\sqrt{x+2}+6\sqrt{x+2}-8\sqrt{x+2}=15$
$\Leftrightarrow 3\sqrt{x+2}=15$
$\Leftrightarrow \sqrt{x+2}=5$
$\Leftrightarrow x+2=25$
$\Leftrightarrow x=23$ (tm)
c.
$\sqrt{(x-2)^2}=12$
$\Leftrightarrow |x-2|=12$
$\Leftrightarrow x-2=12$ hoặc $x-2=-12$
$\Leftrightarrow x=14$ hoặc $x=-10$
e.
PT $\Leftrightarrow |2x-1|-x=3$
Nếu $x\geq \frac{1}{2}$ thì $2x-1-x=3$
$\Leftrightarrow x=4$ (tm)
Nếu $x< \frac{1}{2}$ thì $1-2x-x=3$
$\Leftrightarrow x=\frac{-2}{3}$ (tm)
a) ( x - 3)4 + ( x - 5)4 = 82
Đặt : x - 4 = a , ta có :
( a + 1)4 + ( a - 1)4 = 82
⇔ a4 + 4a3 + 6a2 + 4a + 1 + a4 - 4a3 + 6a2 - 4a + 1 = 82
⇔ 2a4 + 12a2 - 80 = 0
⇔ 2( a4 + 6a2 - 40) = 0
⇔ a4 - 4a2 + 10a2 - 40 = 0
⇔ a2( a2 - 4) + 10( a2 - 4) = 0
⇔ ( a2 - 4)( a2 + 10) = 0
Do : a2 + 10 > 0
⇒ a2 - 4 = 0
⇔ a = + - 2
+) Với : a = 2 , ta có :
x - 4 = 2
⇔ x = 6
+) Với : a = -2 , ta có :
x - 4 = -2
⇔ x = 2
KL.....
b) ( n - 6)( n - 5)( n - 4)( n - 3) = 5.6.7.8
⇔ ( n - 6)( n - 3)( n - 5)( n - 4) = 1680
⇔ ( n2 - 9n + 18)( n2 - 9n + 20) = 1680
Đặt : n2 - 9n + 19 = t , ta có :
( t - 1)( t + 1) = 1680
⇔ t2 - 1 = 1680
⇔ t2 - 412 = 0
⇔ ( t - 41)( t + 41) = 0
⇔ t = 41 hoặc t = - 41
+) Với : t = 41 , ta có :
n2 - 9n + 19 = 41
⇔ n2 - 9n - 22 = 0
⇔ n2 + 2n - 11n - 22 = 0
⇔ n( n + 2) - 11( n + 2) = 0
⇔ ( n + 2)( n - 11) = 0
⇔ n = - 2 hoặc n = 11
+) Với : t = -41 ( giải tương tự )
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a: \(x^3+8x=5x^2+4\)
=>\(x^3-5x^2+8x-4=0\)
=>\(x^3-x^2-4x^2+4x+4x-4=0\)
=>\(x^2\left(x-1\right)-4x\left(x-1\right)+4\left(x-1\right)=0\)
=>\(\left(x-1\right)\left(x^2-4x+4\right)=0\)
=>\(\left(x-1\right)\left(x-2\right)^2=0\)
=>\(\left[{}\begin{matrix}x-1=0\\\left(x-2\right)^2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=2\end{matrix}\right.\)
2: \(x^3+3x^2=x+6\)
=>\(x^3+3x^2-x-6=0\)
=>\(x^3+2x^2+x^2+2x-3x-6=0\)
=>\(x^2\cdot\left(x+2\right)+x\left(x+2\right)-3\left(x+2\right)=0\)
=>\(\left(x+2\right)\left(x^2+x-3\right)=0\)
=>\(\left[{}\begin{matrix}x+2=0\\x^2+x-3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=\dfrac{-1+\sqrt{13}}{2}\\x=\dfrac{-1-\sqrt{13}}{2}\end{matrix}\right.\)
3: ĐKXĐ: x>=0
\(2x+3\sqrt{x}=1\)
=>\(2x+3\sqrt{x}-1=0\)
=>\(x+\dfrac{3}{2}\sqrt{x}-\dfrac{1}{2}=0\)
=>\(\left(\sqrt{x}\right)^2+2\cdot\sqrt{x}\cdot\dfrac{3}{4}+\dfrac{9}{16}-\dfrac{17}{16}=0\)
=>\(\left(\sqrt{x}+\dfrac{3}{4}\right)^2=\dfrac{17}{16}\)
=>\(\left[{}\begin{matrix}\sqrt{x}+\dfrac{3}{4}=-\dfrac{\sqrt{17}}{4}\\\sqrt{x}+\dfrac{3}{4}=\dfrac{\sqrt{17}}{4}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}=\dfrac{\sqrt{17}-3}{4}\left(nhận\right)\\\sqrt{x}=\dfrac{-\sqrt{17}-3}{4}\left(loại\right)\end{matrix}\right.\)
=>\(x=\dfrac{13-3\sqrt{17}}{8}\left(nhận\right)\)
4: \(x^4+4x^2+1=3x^3+3x\)
=>\(x^4-3x^3+4x^2-3x+1=0\)
=>\(x^4-x^3-2x^3+2x^2+2x^2-2x-x+1=0\)
=>\(x^3\left(x-1\right)-2x^2\left(x-1\right)+2x\left(x-1\right)-\left(x-1\right)=0\)
=>\(\left(x-1\right)\left(x^3-2x^2+2x-1\right)=0\)
=>\(\left(x-1\right)\left(x^3-x^2-x^2+x+x-1\right)=0\)
=>\(\left(x-1\right)^2\cdot\left(x^2-x+1\right)=0\)
=>(x-1)^2=0
=>x-1=0
=>x=1
a.
\(x^3+8x=5x^2+4\)
\(\Leftrightarrow x^3-5x^2+8x-4=0\)
\(\Leftrightarrow\left(x^3-4x^2+4x\right)-\left(x^2-4x+4\right)=0\)
\(\Leftrightarrow x\left(x-2\right)^2-\left(x-2\right)^2=0\)
\(\Leftrightarrow\left(x-1\right)\left(x-2\right)^2=0\)
\(\Rightarrow\left[{}\begin{matrix}x=1\\x=2\end{matrix}\right.\)
b.
\(x^3+3x^2-x-6=0\)
\(\Leftrightarrow\left(x^3+x^2-3x\right)+\left(2x^2+2x-6\right)=0\)
\(\Leftrightarrow x\left(x^2+x-3\right)+2\left(x^2+x-3\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x^2+x-3\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=-2\\x=\dfrac{-1\pm\sqrt{13}}{2}\end{matrix}\right.\)