a/ ĐKXĐ: \(x\ge5\)

\(\Leftrightarrow\sqrt{5x^2-14x+9}=5\sqrt{x+1}+\sqrt{x^2-x-20}\)

\(\Leftrightarrow5x^2-14x+9=25x+25+x^2-x-20+10\sqrt{\left(x+1\right)\left(x^2-x-20\right)}\)

\(\Leftrightarrow4x^2-38x+4=10\sqrt{\left(x+1\right)\left(x+4\right)\left(x-5\right)}\)

\(\Leftrightarrow2x^2-19x+2=5\sqrt{\left(x+1\right)\left(x+4\right)\left(x-5\right)}\)

Đến đấy bí, chẳng lẽ lại bình phương giải pt bậc 4.

Nếu đề ban đầu là \(\sqrt{5x^2+14x+9}\) thì có thể tách được

b/ ĐKXĐ: \(x\ge1\)

\(\Leftrightarrow x-1+\sqrt{5+\sqrt{x-1}}=5\)

Đặt \(\left\{{}\begin{matrix}\sqrt{x-1}=a\ge0\\\sqrt{5+\sqrt{x-1}}=b>0\end{matrix}\right.\) \(\Rightarrow\sqrt{5+a}=b\Rightarrow5=b^2-a\)

Phương trình trở thành: \(a^2+b=b^2-a\)

\(\Leftrightarrow a^2-b^2+a+b=0\)

\(\Leftrightarrow\left(a-b\right)\left(a+b\right)+\left(a+b\right)=0\)

\(\Leftrightarrow\left(a-b+1\right)\left(a+b\right)=0\)

\(\Leftrightarrow a+1=b\) (do \(a+b>0\))

\(\Leftrightarrow a+1=\sqrt{a+5}\)

\(\Leftrightarrow a^2+2a+1=a+5\)

\(\Leftrightarrow a^2+a-4=0\Rightarrow a=\frac{-1+\sqrt{17}}{2}\)

\(\Rightarrow\sqrt{x-1}=\frac{-1+\sqrt{17}}{2}\Rightarrow x=\frac{11-\sqrt{17}}{2}\)

\(\Leftrightarrow\sqrt{5x^2+14x+9}-\sqrt{x^2-x-20}-5\sqrt{x+1}=0\)

\(\Rightarrow4x=-7\)

=>x=8

phương trình trên có kq: x=8

bạn trình bày ra được không

a:

\(\Leftrightarrow\sqrt{\left(x-3\right)^2}=3\)

=>|x-3|=3

=>x-3=3 hoặc x-3=-3

=>x=0 hoặc x=6

b: \(\Leftrightarrow\sqrt{x-1+2\sqrt{x-1}+1}=2\)

=>\(\sqrt{\left(\sqrt{x-1}+1\right)^2}=2\)

=>\(\left|\sqrt{x-1}+1\right|=2\)

=>\(\left[{}\begin{matrix}\sqrt{x-1}+1=2\\\sqrt{x-1}+1=-2\left(loại\right)\end{matrix}\right.\Leftrightarrow\sqrt{x-1}=1\)

=>x-1=1

=>x=2

c:

ĐKXĐ: x>4/5

PT \(\Leftrightarrow\sqrt{\dfrac{5x-4}{x+2}}=2\)

=>\(\dfrac{5x-4}{x+2}=4\)

=>5x-4=4x+8

=>x=12(nhận)

d: ĐKXĐ: x-4>=0 và x+1>=0

=>x>=4

PT =>\(\left(\sqrt{x-4}+\sqrt{x+1}\right)^2=5^2=25\)

=>\(x-4+x+1+2\sqrt{\left(x-4\right)\left(x+1\right)}=25\)

=>\(\sqrt{4\left(x^2-3x-4\right)}=25-2x+3=28-2x\)

=>\(\sqrt{x^2-3x-4}=14-x\)

=>x<=14 và x^2-3x-4=(14-x)^2=x^2-28x+196

=>x<=14 và -3x-4=-28x+196

=>x<=14 và 25x=200

=>x=8(nhận)

a) \(\sqrt{x^2-6x+9}=3\)

\(\Leftrightarrow\sqrt{\left(x-3\right)^2}=3\)

\(\Leftrightarrow\left|x-3\right|=3 \)

TH1: \(\left|x-3\right|=x-3\) với \(x\ge3\)

Pt trở thành:

\(x-3=3\) (ĐK: \(x\ge3\))

\(\Leftrightarrow x=3+3\)

\(\Leftrightarrow x=6\left(tm\right)\)

TH2: \(\left|x-3\right|=-\left(x-3\right)\) với \(x< 3\)

Pt trở thành:

\(-\left(x-3\right)=3\) (ĐK: \(x< 3\))

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

\(\Leftrightarrow x=-3+3\)

\(\Leftrightarrow x=0\left(tm\right)\)

b) \(\sqrt{x+2\sqrt{x-1}}=2\) (ĐK: \(x\ge1\))

\(\Leftrightarrow x+2\sqrt{x-1}=4\)

\(\Leftrightarrow2\sqrt{x-1}=4-x\)

\(\Leftrightarrow4\left(x-1\right)=16-8x+x^2\)

\(\Leftrightarrow4x-4=16-8x+x^2\)

\(\Leftrightarrow x^2-12x+20=0\)

\(\Leftrightarrow\left(x-10\right)\left(x-2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=10\left(tm\right)\\x=2\left(tm\right)\end{matrix}\right.\)

c) \(\dfrac{\sqrt{5x-4}}{\sqrt{x+2}}=2\) (ĐK: \(x\ge\dfrac{4}{5}\))

\(\Leftrightarrow\dfrac{5x-4}{x+2}=4\)

\(\Leftrightarrow5x-4=4x+8\)

\(\Leftrightarrow x=12\left(tm\right)\)

Đk: \(x\ge6\)

pt\(\Leftrightarrow\sqrt{5x^2+4x}=5\sqrt{x}+\sqrt{x^2-3x-18}\)

\(\Leftrightarrow5x^2+4x=25x+x^2-3x-18+10\sqrt{x\left(x^2-3x-18\right)}\)

\(\Leftrightarrow2x^2-9x+9=5\sqrt{x^3-3x^2-18x}\)

\(\Leftrightarrow4x^4+81x^2+81-36x^3-162x+36x^2=25\left(x^3-3x^2-18x\right)\)

\(\Leftrightarrow4x^4-61x^3+192x^2+288x+81=0\)

\(\Leftrightarrow\left(x-9\right)\left(4x+3\right)\left(x^2-7x-3\right)=0\)

\(\Leftrightarrow\left(4x+3\right)\left(x-9\right)\left(x-\dfrac{7+\sqrt{61}}{2}\right)\left(x-\dfrac{7-\sqrt{61}}{2}\right)=0\)

mà x \(\ge6\) \(\Rightarrow\left\{{}\begin{matrix}4x+3>0\\x-\dfrac{7-\sqrt{61}}{2}>0\end{matrix}\right.\)

\(\Rightarrow\left(x-9\right)\left(x-\dfrac{7+\sqrt{61}}{2}\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=9\\x=\dfrac{7+\sqrt{61}}{2}\end{matrix}\right.\)

Vậy.....