ê quân,Bạn làm bài này ở phương pháp gì đây,đặt ẩn phụ hay sử dụng BĐT

2: ĐKXĐ: x>=0

\(\sqrt{3x}-2\sqrt{12x}+\dfrac{1}{3}\cdot\sqrt{27x}=-4\)

=>\(\sqrt{3x}-2\cdot2\sqrt{3x}+\dfrac{1}{3}\cdot3\sqrt{3x}=-4\)

=>\(\sqrt{3x}-4\sqrt{3x}+\sqrt{3x}=-4\)

=>\(-2\sqrt{3x}=-4\)

=>\(\sqrt{3x}=2\)

=>3x=4

=>\(x=\dfrac{4}{3}\left(nhận\right)\)

3: 

ĐKXĐ: x>=0

\(3\sqrt{2x}+5\sqrt{8x}-20-\sqrt{18}=0\)

=>\(3\sqrt{2x}+5\cdot2\sqrt{2x}-20-3\sqrt{2}=0\)

=>\(13\sqrt{2x}=20+3\sqrt{2}\)

=>\(\sqrt{2x}=\dfrac{20+3\sqrt{2}}{13}\)

=>\(2x=\dfrac{418+120\sqrt{2}}{169}\)

=>\(x=\dfrac{209+60\sqrt{2}}{169}\left(nhận\right)\)

4: ĐKXĐ: x>=-1

\(\sqrt{16x+16}-\sqrt{9x+9}=1\)

=>\(4\sqrt{x+1}-3\sqrt{x+1}=1\)

=>\(\sqrt{x+1}=1\)

=>x+1=1

=>x=0(nhận)

5: ĐKXĐ: x<=1/3

\(\sqrt{4\left(1-3x\right)}+\sqrt{9\left(1-3x\right)}=10\)

=>\(2\sqrt{1-3x}+3\sqrt{1-3x}=10\)

=>\(5\sqrt{1-3x}=10\)

=>\(\sqrt{1-3x}=2\)

=>1-3x=4

=>3x=1-4=-3

=>x=-3/3=-1(nhận)

6: ĐKXĐ: x>=3

\(\dfrac{2}{3}\sqrt{x-3}+\dfrac{1}{6}\sqrt{x-3}-\sqrt{x-3}=-\dfrac{2}{3}\)

=>\(\sqrt{x-3}\cdot\left(\dfrac{2}{3}+\dfrac{1}{6}-1\right)=-\dfrac{2}{3}\)

=>\(\sqrt{x-3}\cdot\dfrac{-1}{6}=-\dfrac{2}{3}\)

=>\(\sqrt{x-3}=\dfrac{2}{3}:\dfrac{1}{6}=\dfrac{2}{3}\cdot6=\dfrac{12}{3}=4\)

=>x-3=16

=>x=19(nhận)

ĐKXĐ: \(\left\{{}\begin{matrix}x\ge1\\-4+\sqrt{7}\le x\le-1\end{matrix}\right.\)

Khi x thỏa ĐKXĐ, vế phải luôn dương, bình phương 2 vế ta được:

\(\Leftrightarrow3x^2+16x+17+2\sqrt{\left(x^2-1\right)\left(2x^2+16x+18\right)}=4x^2+16x+16\)

\(\Leftrightarrow2\sqrt{\left(x^2-1\right)\left(2x^2+16x+18\right)}=x^2-1\)

\(\Leftrightarrow4\left(x^2-1\right)\left(2x^2+16x+18\right)=\left(x^2-1\right)^2\)

\(\Leftrightarrow\left[{}\begin{matrix}x^2-1=0\\4\left(2x^2+16x+18\right)=x^2-1\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\pm1\\7x^2+64x+73=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\pm1\\x=\dfrac{-32+3\sqrt{57}}{7}\\x=\dfrac{-32-3\sqrt{57}}{7}\left(loại\right)\end{matrix}\right.\)

\(ĐKXĐ:2x^2+16x+18\ge0;x^2-1\ge0\)

\(pt\Leftrightarrow\sqrt{x^2-1}=2x+4-\sqrt{2x^2+16x+18}\)(1)

\(\Leftrightarrow\sqrt{x^2-1}\left(\frac{2\sqrt{x^2-1}}{2x+4+\sqrt{2x^2+16x+18}}\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}\sqrt{x^2-1}=0\\2\sqrt{x^2-1}=2x+4+\sqrt{2x^2+16x+18}\left(2\right)\end{cases}}\)

Lấy(1) + (2), ta được: \(3\sqrt{x^2-1}=4x+8\Leftrightarrow x=\frac{3\sqrt{57}-32}{7}\)

b, \(đk:x\ge2\)

Xét x=2 thay vào pt thấy không thỏa mãn => x>2 hay 27x-54>0

 \(x^3-11x+36x-18=4\sqrt[4]{27x-54}\)

\(\Leftrightarrow27x^3-297x^2+972x-486=4\sqrt[4]{\left(27x-54\right).81.81.81}\le189+27x\) (cosi với 4 số dương, dấu = xảy ra khi x=5)

\(\Leftrightarrow x^3-11x^2+35x-25\le0\)

\(\Leftrightarrow\left(x-1\right)\left(x-5\right)^2\le0\)  (*)

Có \(\left\{{}\begin{matrix}x>2\\\left(x-5\right)^2\ge0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x-1>0\\\left(x-5\right)^2\ge0\end{matrix}\right.\)\(\Rightarrow\left(x-1\right)\left(x-5\right)^2\ge0\) (2*)

Từ (*) và (2*) ,dấu = xra khi x=5 (thỏa mãn)
Vây pt có nghiệm duy nhất x=5

c,Có \(6\sqrt[3]{4x^3+x}=16x^4+5>0\)

\(\Leftrightarrow4x^3+x>0\)

Có: \(16x^4+5=6\sqrt[3]{4x^3+x}\le2\left(4x^3+x+2\right)\) (theo cosi với 3 số dương,dấu = xảy ra khi \(x=\dfrac{1}{2}\))

\(\Leftrightarrow16x^4-8x^3-2x+1\le0\)

\(\Leftrightarrow\left(2x-1\right)^2\left(4x^2+2x+1\right)\le0\) (*)
(tương tự câu b) Dấu = xảy ra khi \(x=\dfrac{1}{2}\)(thỏa mãn)
Vậy....

d) Đk: \(x\ge\dfrac{3}{4}\)

Áp dụng bđt cosi:

 \(\sqrt{2x-1}\le\dfrac{2x-1+1}{2}=x\)

 \(\Rightarrow\dfrac{1}{\sqrt{2x-1}}\ge\dfrac{1}{x}\) (*)

\(\sqrt[4]{4x-3}\le\dfrac{4x-3+1+1+1}{4}=x\)

\(\dfrac{\Rightarrow1}{\sqrt[4]{4x-3}}\ge\dfrac{1}{x}\) (2*)

Từ (*) và (2*) \(\Rightarrow\dfrac{1}{\sqrt{2x-1}}+\dfrac{1}{\sqrt[4]{4x-3}}\ge\dfrac{2}{x}\)

Dấu = xảy ra khi x=1 (tm)

`a)\sqrtx+\sqrt{2-x}=(3x^2-2x+3)/(x^2+1)`

`đk:0<=x<=2`

`pt<=>sqrtx-1+\sqrt{2-x}-1=(3x^2-2x+3)/(x^2+1)-2`

`<=>(x-1)/(sqrtx+1)+(1-x)/(sqrt{2-x}+1)=(x^2-2x+1)/(x^2+1)`

`<=>(x-1)/(sqrtx+1)+(1-x)/(sqrt{2-x}+1)=(x-1)^2/(x^2+1)`

`<=>(x-1)((x-1)/(x^2+1)+1/(sqrt{2-x}+1)-1/(sqrtx+1))=0`

`<=>x-1=0<=>x=1`

Vậy `S={1}`

1) ĐK: \(x\ge\frac{3}{2}\)

pt \(\Leftrightarrow\frac{2x-2-\left(6x-9\right)}{\sqrt{2x-2}+\sqrt{6x-9}}=16x^2-28x-20x+35\)

\(\Leftrightarrow\frac{-4x+7}{\sqrt{2x-2}+\sqrt{6x-9}}=4x\left(4x-7\right)-5\left(4x-7\right)\)

\(\Leftrightarrow-\frac{4x-7}{\sqrt{2x-2}+\sqrt{6x-9}}=\left(4x-7\right)\left(4x-5\right)\)

\(\Leftrightarrow\left(4x-7\right)\left(\frac{1}{\sqrt{2x-2}+\sqrt{6x-9}}+4x-5\right)=0\)

\(\Leftrightarrow4x-7=0\Leftrightarrow x=\frac{7}{4}\) (nhận)

2) ĐK: \(2\le x\le4\)

pt \(\Leftrightarrow\sqrt{x-2}+\sqrt{a-x}=2\left(x^2-6x+9\right)+7x-19\)

\(\Leftrightarrow\sqrt{x-2}-\left(7x-20\right)+\sqrt{4-x}-1=2\left(x-3\right)^2\)

\(\Leftrightarrow\frac{x-2-\left(7x-20\right)^2}{\sqrt{x-2}+7x-20}+\frac{4-x-1}{\sqrt{4-x}+1}=2\left(x-3\right)^2\)

\(\Leftrightarrow\frac{\left(x-3\right)\left(134-49x\right)}{\sqrt{x-2}+\left(7x-20\right)}+\frac{3-x}{\sqrt{4-x}+1}=2\left(x-3\right)^2\)

\(\Leftrightarrow x-3=0\Leftrightarrow x=3\) (nhận)

\(\sqrt{2x^2+16x+18}+\sqrt{x^2+1}=2x+4\left(1\right)\)

\(ĐK:x\in R\)

\(pt\left(1\right)\Leftrightarrow2x^2+16x+18+x^2+1+2\sqrt[]{(2x^2+16x+18)\left(x^2+1\right)}=4x^2+16x+16\)

\(\Leftrightarrow3+2\sqrt{(2x^2+16x+18)\left(x^2+1\right)}=x^2\)

\(\Leftrightarrow2\sqrt{(2x^2+16x+8)\left(x^2+1\right)}=x^2-3\)

\(\Leftrightarrow\left\{{}\begin{matrix}x^2-3\ge0\\4\left(2x^2+16x+8\right)\left(x^2+1\right)=x^4-6x^2+9\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}-\sqrt{3}\le x\le\sqrt{3}\\4\left(2x^4+16x^3+10x^2+16x+8\right)=x^4-6x^2+9\end{matrix}\right.\)

\(\Leftrightarrow7x^4+64x^3+46x^2+64x+23=0\)