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\(\sqrt{4x^2}=3\left(ĐK:4x^2\ge0\forall x\in R\right)\\ \Leftrightarrow\sqrt{\left(2x\right)^2}=3\\ \Leftrightarrow\left|2x\right|=3\\ \Leftrightarrow\left[{}\begin{matrix}2x=-3\\2x=3\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{3}{2}\left(tm\right)\\x=\dfrac{3}{2}\left(tm\right)\end{matrix}\right.\)
Vậy \(S=\left\{-\dfrac{3}{2};\dfrac{3}{2}\right\}\)
\(\sqrt{x^2-6x+9}=2\\ \Leftrightarrow\sqrt{\left(x-3\right)^2}=2\left(ĐK:\left(x-3\right)^2\ge0\forall x\in R\right)\\ \Leftrightarrow\left|x-3\right|=2\\ \Leftrightarrow\left[{}\begin{matrix}x-3=2\\x-3=-2\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=2+3\\x=-2-3\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=5\left(tm\right)\\x=-5\left(tm\right)\end{matrix}\right.\)
Vậy \(S=\left(\pm5\right)\)
\(\sqrt{\left(2x-3\right)^2}=6\left(ĐK:\left(2x-3\right)^2\ge0\forall x\in R\right)\\ \Leftrightarrow\left|2x-3\right|=6\\ \Leftrightarrow\left[{}\begin{matrix}2x-3=6\\2x-3=-6\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}2x=3+6\\2x=-6+3\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}2x=9\\2x=-3\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=4,5\left(tm\right)\\x=-1,5\left(tm\right)\end{matrix}\right.\)
Vậy \(S=\left\{4,5;-1,5\right\}\)
\(\sqrt{25x^2}=100\\ \sqrt{\left(5x\right)^2}=100\left(ĐK:\left(5x\right)^2\ge0\forall x\in R\right)\\\Leftrightarrow \left|5x\right|=100\\ \Leftrightarrow\left[{}\begin{matrix}5x=100\\5x=-100\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=20\left(tm\right)\\x=-20\left(tm\right)\end{matrix}\right.\)
Vậy \(S=\left\{\pm20\right\}\)
b)\(\sqrt{25x^2}=19\)
\(\Leftrightarrow5x=19\)
\(\Leftrightarrow x=\dfrac{19}{5}\)
c)\(\sqrt{x-7}+3=0\)
\(\Leftrightarrow\sqrt{x-7}=-3\)
\(\Leftrightarrow x-7=9\)
\(\Leftrightarrow x=16\)
\(\left\{{}\begin{matrix}x^2+2xy-3y^2=-4\left(1\right)\\2x^2+xy+4y^2=5\left(2\right)\end{matrix}\right.\)\(với\)\(y=0\Rightarrow hpt\Leftrightarrow\left\{{}\begin{matrix}x^2=-4\\2x^2=5\end{matrix}\right.\)\(\left(loại\right)\)
\(y\ne0\) \(đặt:x=t.y\Rightarrow hpt\Leftrightarrow\left\{{}\begin{matrix}t^2y^2+2ty^2-3y^2=-4\left(3\right)\\2t^2y^2+ty^2+4y^2=5\left(4\right)\end{matrix}\right.\)
\(\Leftrightarrow5t^2y^2+10ty^2-15y^2=-8t^2y^2-4ty^2-16y^2\)
\(\Leftrightarrow13t^2y^2+14ty^2+y^2=0\)
\(\Leftrightarrow13t^2+14t+1=0\Leftrightarrow\left[{}\begin{matrix}t=-\dfrac{1}{13}\\t=-1\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{1}{13}y\left(5\right)\\x=-y\left(6\right)\end{matrix}\right.\)
\(thay\left(5\right)và\left(6\right)\) \(lên\left(1\right)hoặc\left(2\right)\Rightarrow\left(x;y\right)=\left\{\left(1;-1\right);\left(-1;1\right);\left(-\dfrac{1}{\sqrt{133}};\dfrac{13}{\sqrt{133}}\right)\right\}\)
\(pt:x^4-4x^3+x^2+6x+m+2=0\)
\(\Leftrightarrow x^4-4x^3+4x^2-3x^2+6x+m+2=0\)
\(\Leftrightarrow\left(x^2-2x\right)^2-3\left(x^2-2x\right)+m+2=0\left(1\right)\)
\(đặt:x^2-2x=t\ge-1\)
\(\Rightarrow\left(1\right)\Leftrightarrow t^2-3t=-m-2\)
\(xét:f\left(t\right)=t^2-3t\) \(trên[-1;+\text{∞})\) \(và:y=-m-2\)
\(\Rightarrow f\left(-1\right)=4\)
\(f\left(-\dfrac{b}{2a}\right)=-\dfrac{9}{4}\)
\(\left(1\right)\) \(có\) \(3\) \(ngo\) \(pb\Leftrightarrow-m-2=4\Leftrightarrow m=-6\)
Bài 1: Giải phương trình
a) ĐKXĐ: \(x\ge3\)
Ta có: \(\sqrt{100\cdot\left(x-3\right)}=\sqrt{20}\)
\(\Leftrightarrow\left|100\cdot\left(x-3\right)\right|=\left|20\right|\)
\(\Leftrightarrow100\cdot\left|x-3\right|=20\)
\(\Leftrightarrow\left|x-3\right|=\frac{1}{5}\)
\(\Leftrightarrow\left[{}\begin{matrix}x-3=\frac{1}{5}\\x-3=-\frac{1}{5}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\frac{16}{5}\left(nhận\right)\\x=\frac{14}{5}\left(loại\right)\end{matrix}\right.\)
Vậy: \(S=\left\{\frac{16}{5}\right\}\)
b) Ta có: \(\sqrt{\left(x-3\right)^2}=7\)
\(\Leftrightarrow\left|x-3\right|=7\)
\(\Leftrightarrow\left[{}\begin{matrix}x-3=7\\x-3=-7\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=10\\x=-4\end{matrix}\right.\)
Vậy: S={10;-4}
c) Ta có: \(\sqrt{4x^2+4x+1}=6\)
\(\Leftrightarrow\sqrt{\left(2x+1\right)^2}=6\)
\(\Leftrightarrow\left|2x+1\right|=6\)
\(\Leftrightarrow\left[{}\begin{matrix}2x+1=6\\2x+1=-6\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x=5\\2x=-7\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\frac{5}{2}\\x=\frac{-7}{2}\end{matrix}\right.\)
Vậy: \(S=\left\{\frac{5}{2};\frac{-7}{2}\right\}\)
a, ĐKXĐ: \(x^2-4x+4\ge0\Rightarrow\left(x-2\right)^2\ge0\left(luônđúng\right)\)
\(\sqrt{x^2-4x+4}=1\\ \Rightarrow x-2=1\\ \Rightarrow x=3\)
b,\(ĐKXĐ:1-4x+4x^2\ge0\Rightarrow\left(1-2x\right)^2\ge0\left(luônđúng\right)\)
\(\sqrt{1-4x+4x^2}=5\\ \Rightarrow\left|1-2x\right|=5\\ \Rightarrow\left[{}\begin{matrix}1-2x=5\\1-2x=-5\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=-2\\x=3\end{matrix}\right.\)
d, ĐKXĐ: \(\left\{{}\begin{matrix}9x^2\ge0\\2x+1\ge0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x\ge0\\x\ge-\dfrac{1}{2}\end{matrix}\right.\Rightarrow x\ge0\)
\(\sqrt{9x^2}=2x+1\\ \Rightarrow\left|3x\right|=2x+1\\ \Rightarrow\left[{}\begin{matrix}3x=2x+1\\3x=-2x+1\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=1\\x=\dfrac{1}{5}\end{matrix}\right.\)
c, ĐKXĐ: \(1-2x+x^2\ge0\Rightarrow\left(1-x\right)^2\ge0\left(luônđúng\right)\)
\(\sqrt{1-2x+x^2}-6=0\\ \Rightarrow\left|1-x\right|=6\\ \Rightarrow\left[{}\begin{matrix}1-x=-6\\1-x=6\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=7\\x=-5\end{matrix}\right.\)
e, \(\left\{{}\begin{matrix}9-6x+x^2\ge0\\x\ge0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}\left(3-x\right)^2\ge0\left(luônđúng\right)\\x\ge0\end{matrix}\right.\)\(\Rightarrow x\ge0\)
\(\sqrt{9-6x+x^2}=x\\ \Rightarrow\left|3-x\right|=x\\ \Rightarrow\left[{}\begin{matrix}3-x=-x\\3-x=x\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}3=0\left(vôlí\right)\\x=1,5\end{matrix}\right.\)
a: ĐKXĐ: x>=-3/2
\(\sqrt{x^2+4}=\sqrt{2x+3}\)
=>\(x^2+4=2x+3\)
=>\(x^2-2x+1=0\)
=>\(\left(x-1\right)^2=0\)
=>x-1=0
=>x=1(nhận)
b: \(\sqrt{x^2-6x+9}=2x-1\)(ĐKXĐ: \(x\in R\))
=>\(\sqrt{\left(x-3\right)^2}=2x-1\)
=>\(\left\{{}\begin{matrix}\left(2x-1\right)^2=\left(x-3\right)^2\\x>=\dfrac{1}{2}\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}\left(2x-1-x+3\right)\left(2x-1+x-3\right)=0\\x>=\dfrac{1}{2}\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}\left(x+2\right)\left(3x-4\right)=0\\x>=\dfrac{1}{2}\end{matrix}\right.\)
=>x=4/3(nhận) hoặc x=-2(loại)
c:
Sửa đề: \(\sqrt{4x+12}=\sqrt{9x+27}-5\)
ĐKXĐ: \(x>=-3\)
\(\sqrt{4x+12}=\sqrt{9x+27}-5\)
=>\(2\sqrt{x+3}=3\sqrt{x+3}-5\)
=>\(-\sqrt{x+3}=-5\)
=>x+3=25
=>x=22(nhận)
d: ĐKXĐ: \(\left[{}\begin{matrix}x< =\dfrac{3-\sqrt{5}}{4}\\x>=\dfrac{3+\sqrt{5}}{4}\end{matrix}\right.\)
\(\sqrt{4x^2-6x+1}=\left|2x-5\right|\)
=>\(\sqrt{\left(4x^2-6x+1\right)}=\sqrt{4x^2-20x+25}\)
=>\(4x^2-6x+1=4x^2-20x+25\)
=>\(-6x+20x=25-1\)
=>\(14x=24\)
=>x=12/7(nhận)
c) (d tương tự)
\(\sqrt[3]{7-16x}=a;\text{ }\sqrt{2x+8}=b\Rightarrow a^3+8b^2=71\)
và \(a+2b=5\)
--> Thế
\(a\text{) }\sqrt{1-x^2}=y\Rightarrow x^2+y^2=1\)
Mà \(x^3+y^3=\sqrt{2}xy\Rightarrow\left(x^3+y^3\right)^2=2x^2y^2=2x^2y^2\left(x^2+y^2\right)\text{ (*)}\)
Tới đây có dạng đẳng cấp, có thể phân tích nhân tử hoặc chia xuống.
y = 0 thì x = 1 (không thỏa pt ban đầu)
Xét y khác 0. Chia cả 2 vế của (*) cho y6:
\(\text{(*)}\Leftrightarrow\left(\frac{x^3}{y^3}+1\right)^2=2\frac{x^2}{y^2}\left(\frac{x^2}{y^2}+1\right)\)\(\Leftrightarrow\left(\frac{x}{y}-1\right)\left[\left(\frac{x}{y}\right)^5+\left(\frac{x}{y}\right)^4+\left(\frac{x}{y}\right)^3+3\left(\frac{x}{y}\right)^2+\frac{x}{y}-1\right]=0\)
Không khả quan lắm :)) bạn tự tìm cách khác nhé.
a)
DK: x\(\ge\)-2,x\(\ge\)\(\dfrac{1}{2}\)
=>\(\sqrt{4\left(x+2\right)}-\sqrt{2x-1}+\sqrt{9\left(x+2\right)}=0\)
\(\Leftrightarrow2\sqrt{x+2}-\sqrt{2x-1}+3\sqrt{x+2}=0\)
\(\Leftrightarrow5\sqrt{x+2}-\sqrt{2x-1}=0\)
\(\Leftrightarrow5\sqrt{x+2}=\sqrt{2x-1}\)
<=>25x+50=2x-1
=>23x=-51
=>x=\(-\dfrac{51}{23}\)(ko thỏa mãn dk)
=> phương trình vô nghiệm..
b)
ĐKXĐ:\(x\ge1,x\ge-1\)
\(\Leftrightarrow\sqrt{\left(x+1\right)\left(x-1\right)}-3\sqrt{x-1}=0\)
\(\Leftrightarrow\sqrt{x-1}\left(\sqrt{x+1}-3\right)=0\)
\(\Rightarrow\left\{{}\begin{matrix}\sqrt{x-1}=0\\\sqrt{x+1}-3=0\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x=1\\x=8\end{matrix}\right.\)(nhận)
Vậy S={1;8}
c) ĐKXĐ:
\(x\ge0\)
\(\Leftrightarrow6-9\sqrt{2x}-2\sqrt{2x}+6x=6x-5\)
\(\Leftrightarrow-11\sqrt{2x}=-11\)
\(\Leftrightarrow\sqrt{2x}=1\)
\(\Leftrightarrow2x=1\\ \Leftrightarrow x=\dfrac{1}{2}\)
Câu a :\(\sqrt{4x+8}-2\sqrt{2x-1}+\sqrt{9x+18}=0\) ( ĐK : \(x\ge\dfrac{1}{2}\) )
\(\Leftrightarrow\sqrt{4x+8}+\sqrt{9x+18}=\sqrt{2x-1}\)
\(\Leftrightarrow2\sqrt{x+2}+3\sqrt{x+2}=\sqrt{2x-1}\)
\(\Leftrightarrow5\sqrt{x+2}=\sqrt{2x-1}\)
\(\Leftrightarrow25\left(x+2\right)=2x-1\)
\(\Leftrightarrow25x+50=2x-1\)
\(\Leftrightarrow23x=-51\)
\(\Leftrightarrow x=-\dfrac{51}{23}< -\dfrac{1}{2}\)
Vậy phương trình vô nghiệm .
Câu b :
\(\sqrt{x^2-1}-\sqrt{9\left(x-1\right)}=0\) ( ĐK : \(x\ge1\) )
\(\Leftrightarrow\sqrt{\left(x-1\right)\left(x+1\right)}-3\sqrt{\left(x-1\right)}=0\)
\(\Leftrightarrow\sqrt{\left(x-1\right)}\left(\sqrt{x+1}-3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x-1}=0\\\sqrt{x+1}-3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=8\end{matrix}\right.\)
Vậy \(S=\left\{1;8\right\}\)
Câu c : \(\left(3-\sqrt{2x}\right)\left(2-3\sqrt{2x}\right)=6x-5\) ( ĐK : \(x\ge\dfrac{5}{6}\) )
\(\Leftrightarrow6-9\sqrt{2x}-2\sqrt{2x}+6x=6x-5\)
\(\Leftrightarrow-11\sqrt{2x}+11=0\)
\(\Leftrightarrow-11\left(\sqrt{2x}-1\right)=0\)
\(\Leftrightarrow\sqrt{2x}-1=0\)
\(\Leftrightarrow x=\dfrac{1}{2}\left(TMĐK\right)\)
Vậy \(S=\left\{\dfrac{1}{2}\right\}\)
Chúc bạn học tốt
a
\(\sqrt{9\left(2-3x\right)^2}=6\\ \Leftrightarrow3\left|2-3x\right|=6\\ \Leftrightarrow\left|2-3x\right|=2\)
Với \(x\le\dfrac{2}{3}\) thì PT trở thành:
\(2-3x=2\\ \Leftrightarrow3x=0\\ \Leftrightarrow x=0\left(nhận\right)\)
Với \(x>\dfrac{2}{3}\) thì PT trở thành:
\(3x-2=2\\ \Leftrightarrow3x=4\\ \Leftrightarrow x=\dfrac{4}{3}\left(nhận\right)\)
b
ĐK: \(x\ge-\dfrac{3}{2}\)
\(\sqrt{4x^2-9}=2\sqrt{2x+3}\\ \Leftrightarrow\sqrt{\left(2x\right)^2-3^2}=2\sqrt{2x+3}\\ \Leftrightarrow\sqrt{2x-3}.\sqrt{2x+3}-2\sqrt{2x+3}=0\\ \Leftrightarrow\sqrt{2x+3}\left(\sqrt{2x-3}-2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}\sqrt{2x+3}=0\\\sqrt{2x-3}-2=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{3}{2}\\2x-3=4\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{3}{2}\left(nhận\right)\\x=\dfrac{7}{2}\left(nhận\right)\end{matrix}\right.\)
c
ĐK: \(x\ge3\)
\(\sqrt{10\left(x-3\right)}=\sqrt{20}\\ \Leftrightarrow10\left(x-3\right)=20\\ \Leftrightarrow x-3=2\\ \Leftrightarrow x=5\left(nhận\right)\)
d
\(\sqrt{x^2+6x+9}=3x-6\\ \Leftrightarrow\sqrt{\left(x+3\right)^2}=3x-6\\ \Leftrightarrow\left|x+3\right|=3x-6\)
Với \(x\ge-3\) thì PT trở thành:
\(x+3=3x-6\\ \Leftrightarrow x+3-3x+6=0\\ \Leftrightarrow-2x+9=0\\ \Leftrightarrow x=\dfrac{9}{2}\left(nhận\right)\)
Với \(x< -3\) thì PT trở thành:
\(-x-3=3x-6\\ \Leftrightarrow-x-3-3x+6=0\\ \Leftrightarrow-2x+3=0\\ \Leftrightarrow x=\dfrac{3}{2}\left(loại\right)\)
a, Ta có: \(\Delta'=1-m+3=4-m\)
Phương trình có 2 nghiệm phân biệt \(\Leftrightarrow\Delta'>0\Leftrightarrow4-m>0\Leftrightarrow m< 4\)
b, ĐXXĐ: \(x\le\frac{9}{4}\)
\(pt\Leftrightarrow\sqrt{\left(9-4x\right)\left(x-3\right)^2}=\left|-2x+5\right|\sqrt{9-4x}\)
\(\Leftrightarrow\sqrt{9-4x}\left(\left|x-3\right|-\left|-2x+5\right|\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}9-4x=0\\\left|x-3\right|=\left|-2x+5\right|\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}9-4x=0\\x-3=-2x+5\\x-3=2x-5\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\frac{9}{4}\\x=\frac{8}{3}\left(l\right)\\x=2\end{matrix}\right.\)
Vậy pt đã cho có 2 nghiệm \(x=2;x=\frac{9}{4}\)