\(-2\left(\sqrt{1+x}+\sqrt{1-x}\right)+7=\sqrt{\left(5-2x\right)\left(5+2x\right)}-2\sqrt{1-x^2}\)

ĐKCĐ: \(-1\le x\le1\)

\(\Leftrightarrow2\left(\sqrt{\left(1-x\right)}-1\right)\left(\sqrt{1+x}-1\right)+5-\sqrt{\left(5-2x\right)\left(5+2x\right)}=0\)

 \(\Leftrightarrow2x^2\left[\frac{2}{5+\sqrt{\left(5-2x\right)\left(5+2x\right)}}-\frac{1}{\left(\sqrt{1-x}+1\right)\left(\sqrt{1+x}+1\right)}\right]\)

Đặt: \(A=\frac{2}{5+\sqrt{\left(5-2x\right)\left(5+2x\right)}}-\frac{1}{\left(\sqrt{1-x}+1\right)\left(\sqrt{1+x}+1\right)}\)

Có: \(A\le\frac{2}{5+\sqrt{\left(5-2\right)\left(5-2\right)}}-\frac{1}{\sqrt{1-x^2}+1+\sqrt{1-x}+\sqrt{1+x}}< \frac{2}{5+3}-\frac{1}{1+1+2}=0\)

\(\Rightarrow x=0\) là nghiệm của pt

x=0. Ai giúp với
 

Mấy ché k giúp ak.

\(ĐK:\frac{2}{3}\ge x\ge\frac{5}{2}\)

\(PT\Leftrightarrow\left(4x^2-4x+1\right)+\left(2x-5\right)\sqrt{2+4x}-\left(2x+3\right)\sqrt{6-4x}+16=0\)

\(\Leftrightarrow\left(2x-1\right)^2+\left(2x-5\right)\sqrt{2+4x}-\left(2x+3\right)\sqrt{6-4x}+16=0\)

\(\Leftrightarrow\left(2x-1\right)^2+\left(2x-5\right)\left(\sqrt{2+4x}-2\right)-\left(2x+3\right)\left(\sqrt{6-4x}-2\right)=0\)

\(\Leftrightarrow\left(2x-1\right)^2+\left(2x-5\right)\frac{2+4x-4}{\sqrt{2+4x}+2}+\left(2x+3\right)\frac{6-4x-4}{\sqrt{6-4x}+2}=0\)

\(\Leftrightarrow\left(2x-1\right)^2+\left(2x-5\right)\frac{2\left(2x-1\right)}{\sqrt{2+4x}+2}+\left(2x+3\right)\frac{-2\left(2x-1\right)}{\sqrt{6-4x}+2}=0\)

\(\Leftrightarrow\left(2x-1\right)\left(2x-1+\left(2x-5\right)\frac{2}{\sqrt{2+4x}+2}+\left(2x+3\right)\frac{-2}{\sqrt{6-4x}+2}\right)=0\)

Theo ĐK ta chứng minh đc \(\left(2x-1+\left(2x-5\right)\frac{2}{\sqrt{2+4x}+2}+\left(2x+3\right)\frac{-2}{\sqrt{6-4x}+2}\right)>0\)

Do đó \(2x-1=0\Rightarrow x=\frac{1}{2}\left(TMĐKXĐ\right)\)

ĐKXĐ: \(x>0\)

Ta có:

\(-\sqrt{x}-2\left(x-\frac{1}{x}\right)=\frac{1}{2x^3}-\frac{1}{2x\sqrt{x}}\)

\(\Leftrightarrow-\sqrt{x}+\frac{1}{2x\sqrt{x}}=\frac{1}{2x^3}+2x-\frac{2}{x}\)

\(\frac{\Leftrightarrow1}{2x\sqrt{x}}-\sqrt{x}=2\left(x-\frac{1}{x}+\frac{1}{4x^3}\right)\)

Đặt : \(\frac{1}{2x\sqrt{x}}-\sqrt{x}=a\Rightarrow a^2=x-\frac{1}{x}+\frac{1}{4x^3}\)

Khi đó pt đã cho trở thành:

\(a=2a^2\Leftrightarrow\orbr{\begin{cases}a=0\\a=\frac{1}{2}\end{cases}}\)

+) a = 0\(\Rightarrow x=\frac{1}{\sqrt{2}}\)

Tương tự

ĐKXĐ : \(0\le x\le1\)

Đặt \(\sqrt{x}=a;\sqrt{1-x}=b\left(a;b\ge0\right)\)

Khi đó ta được a² + b² = 1 (1)

Lại có phương trình ban đầu trở thành 

\(\dfrac{2a^3}{a+b}+ab=1\) (2) 

Từ (1) ; (2) ta được \(\dfrac{2a^3}{a+b}+ab=a^2+b^2\)

\(\Leftrightarrow2a^3=\left(a+b\right).\left(a^2-ab+b^2\right)\)

\(\Leftrightarrow a^3=b^3\Leftrightarrow a=b\)

Khi đó \(\sqrt{x}=\sqrt{1-x}\Leftrightarrow x=1-x\Leftrightarrow x=\dfrac{1}{2}\left(tm\right)\)

Vậy tập nghiệm \(S=\left\{\dfrac{1}{2}\right\}\)

ĐK: \(\hept{\begin{cases}x^3+2x+4\ge0\\x^3-2x+4\ge0\end{cases}}\)

Đặt: \(\hept{\begin{cases}a=\sqrt{x^3+2x+4}\left(a\ge0\right)\\b=\sqrt{x^3-2x+4}\left(b\ge0\right)\end{cases}\Rightarrow\hept{\begin{cases}a^2=x^3+2x+4\\b^2=x^3-2x+4\end{cases}}\Rightarrow a^2-b^2=4x\Rightarrow x=\frac{a^2-b^2}{4}}\) 

\(pt\Leftrightarrow\left[1+\left(\frac{a^2-b^2}{4}\right)\right]a+\left[1-\left(\frac{a^2-b^2}{4}\right)\right]b=4\) 

\(\Leftrightarrow\left(4+a^2-b^2\right)a+\left(4-a^2+b^2\right)b=16\)

\(\Leftrightarrow a^3+b^3-ab^2-a^2b+4\left(a+b\right)=16\)

\(\Leftrightarrow\left(a+b\right)\left(a^2-ab+b^2\right)-ab\left(a+b\right)+4\left(a+b\right)=16\)

\(\Leftrightarrow\left(a+b\right)\left(a^2-2ab+b^2\right)+4\left(a+b\right)=16\)

\(\Leftrightarrow\left(a+b\right)\left(a-b\right)^2+4\left(a+b\right)=16\) (1)

Từ pt, ta có: \(\left(1+x\right)a-\left(1-x\right)b=4\)

\(\Leftrightarrow a+b+\left(a-b\right)x=4\) (2)

Thay (1) và (2) vào, ta có:

\(\left(a+b\right)\left(a-b\right)^2+4\left(a+b\right)=4\left[a+b+\left(a-b\right)x\right]\)

\(\Leftrightarrow\left(a+b\right)\left(a-b\right)^2=4\left(a-b\right)x\)

\(\Leftrightarrow\left(a-b\right)\left[\left(a+b\right)\left(a-b\right)-4x\right]=0\)

\(\Leftrightarrow\left(a-b\right)\left(a^2-b^2-4x\right)=0\Leftrightarrow\orbr{\begin{cases}a=b\\a^2-b^2=4x\end{cases}}\)

Với \(a=b\) , ta có: \(\sqrt{x^3+2x+4}=\sqrt{x^3-2x+4}\Leftrightarrow x=0\left(TM\right)\)

Với \(a^2-b^2=4x\) , ta có: \(x^3+2x+4-\left(x^3-2x+4\right)=4x\)

\(\Leftrightarrow4x=0\)

\(\Rightarrow x=0\)

Vậy:.........

Lớp mấy đây, lớp 8 mà đây á

tớ ra =0 cậu k cho mình nhé

ĐKXĐ: \(x\ge-3\)

\(\Leftrightarrow\left(2x-1\right)x-\left(2x-1\right)\sqrt{x+3}-x^2+x+3=0\)

\(\Leftrightarrow\left(2x-1\right)\left(x-\sqrt{x+3}\right)-\left(x^2-x-3\right)=0\)

\(\Rightarrow\frac{\left(2x-1\right)\left(x^2-x-3\right)}{x+\sqrt{x+3}}-\left(x^2-x-3\right)=0\)

\(\Leftrightarrow\left(x^2-x-3\right)\left(\frac{2x-1}{x+\sqrt{x+3}}-1\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x^2-x-3=0\\\frac{2x-1}{x+\sqrt{x+3}}=1\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x^2-x-3=0\\x-1=\sqrt{x+3}\left(1\right)\end{matrix}\right.\)

\(\left(1\right)\Leftrightarrow\left\{{}\begin{matrix}x\ge1\\\left(x-1\right)^2=x+3\end{matrix}\right.\)

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