\(\sqrt[3]{1945x+1975}+\sqrt[3]{72x+13}+\sqrt[3]{30-x}-\sqrt[3]{2017+2018}=0\)

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NV
7 tháng 11 2019

a/ ĐKXĐ: \(-\frac{1}{2}\le x\le4\)

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

\(\Leftrightarrow4-x=3x+2+2\sqrt{2x^2+3x+1}\)

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

\(\Leftrightarrow4x^2-4x+1=2x^2+3x+1\)

\(\Leftrightarrow2x^2-7x=0\Rightarrow\left[{}\begin{matrix}x=0\\x=\frac{7}{2}\left(l\right)\end{matrix}\right.\)

Bài này liên hợp cũng được

b/ ĐKXĐ: ...

\(\Leftrightarrow\sqrt{5x+1}^2-\sqrt{5x+1}\left(\sqrt{14x+7}-\sqrt{2x+3}\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}5x+1=0\Rightarrow x=-\frac{1}{5}\\\sqrt{5x+1}-\sqrt{14x+7}+\sqrt{2x+3}=0\left(1\right)\end{matrix}\right.\)

\(\left(1\right)\Leftrightarrow\sqrt{5x+1}+\sqrt{2x+3}=\sqrt{14x+7}\)

\(\Leftrightarrow7x+4+2\sqrt{10x^2+17x+3}=14x+7\)

\(\Leftrightarrow2\sqrt{10x^2+17x+3}=7x+3\)

\(\Leftrightarrow4\left(10x^2+17x+3\right)=\left(7x+3\right)^2\)

\(\Leftrightarrow...\)

NV
7 tháng 11 2019

c/ ĐKXĐ: \(x\ge\frac{1}{2}\)

Đặt \(\left\{{}\begin{matrix}\sqrt[3]{2-2x}=a\\\sqrt{2x-1}=b\end{matrix}\right.\) ta được:

\(\left\{{}\begin{matrix}a=1-b\\a^3+b^2=1\end{matrix}\right.\) \(\Rightarrow a^3+\left(1-a\right)^2=1\)

\(\Leftrightarrow a^3+a^2-2a=0\)

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

\(\Rightarrow\left[{}\begin{matrix}2-2x=0\\2-2x=1\\2-2x=-8\end{matrix}\right.\)

d/ ĐKXĐ: \(x\le\frac{5}{4}\)

Đặt \(\left\{{}\begin{matrix}\sqrt{5-4x}=a\\\sqrt[3]{x+7}=b\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}a+b=3\\a^2+4b^3=33\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}a=3-b\\a^2+4b^3=33\end{matrix}\right.\)

\(\Leftrightarrow\left(3-b\right)^2+4b^3=33\)

\(\Leftrightarrow4b^3+b^2-6b-24=0\)

\(\Leftrightarrow\left(b-2\right)\left(4b^2+9b+12\right)=0\)

\(\Rightarrow b=2\Rightarrow\sqrt[3]{x+7}=2\Rightarrow x=1\)

NV
26 tháng 11 2019

a/ ĐKXĐ: \(-\frac{3}{2}\le x\le4\)

\(\sqrt{2x+3}+\sqrt{4-x}=6x-3\left(x+7-2\sqrt{\left(2x+3\right)\left(4-x\right)}\right)-10\)

\(\Leftrightarrow\sqrt{2x+3}+\sqrt{4-x}=3\left(x+7+2\sqrt{\left(2x+3\right)\left(4-x\right)}\right)-52\)

Đặt \(\sqrt{2x+3}+\sqrt{4-x}=a>0\Rightarrow a^2=x+7+2\sqrt{\left(2x+3\right)\left(4-x\right)}\)

Phương trình trở thành:

\(a=3a^2-52\Leftrightarrow3a^2-a-52=0\Rightarrow\left[{}\begin{matrix}a=-4\left(l\right)\\a=\frac{13}{3}\end{matrix}\right.\)

\(\sqrt{2x+3}+\sqrt{4-x}=\frac{13}{3}\)

Phương trình này vô nghiệm nên ko muốn giải tiếp, bạn bình phương lên và chuyển vế thôi :(

b/ ĐKXĐ: \(-\frac{1}{4}\le x\le1\)

Đặt \(\sqrt{4x+1}+2\sqrt{1-x}=a>0\Rightarrow a^2=5+4\sqrt{-4x^2+3x+1}\)

\(\Rightarrow\sqrt{-4x^2+3x+1}=\frac{a^2-5}{4}\)

Pt trở thành:

\(a+10\left(\frac{a^2-5}{4}\right)=13\)

\(\Leftrightarrow5a^2+2a-51=0\Rightarrow\left[{}\begin{matrix}a=3\\a=-\frac{17}{5}\left(l\right)\end{matrix}\right.\)

\(\Rightarrow\sqrt{-4x^2+3x+1}=\frac{a^2-5}{4}=1\)

\(\Leftrightarrow-4x^2+3x=0\Rightarrow\left[{}\begin{matrix}x=0\\x=\frac{3}{4}\end{matrix}\right.\)

NV
26 tháng 11 2019

c/ \(\Leftrightarrow x^2\left(x^2+2\right)=12-x\sqrt{2x^2+4}\)

\(\Leftrightarrow x^2\left(2x^2+4\right)=24-2x\sqrt{2x^2+4}\)

Đặt \(x\sqrt{2x^2+4}=a\) ta được:

\(a^2=24-2a\Leftrightarrow a^2+2a-24=0\Leftrightarrow\left[{}\begin{matrix}a=4\\a=-6\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x\sqrt{2x^2+4}=4\left(x>0\right)\\x\sqrt{2x^2+4}=-6\left(x< 0\right)\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x^2\left(2x^2+4\right)=16\\x^2\left(2x^2+4\right)=36\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x^4+2x^2-8=0\\x^4+2x^2-18=0\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x^2=2\\x^2=-4\left(l\right)\\x^2=\sqrt{19}-1\\x^2=-\sqrt{19}-1\left(l\right)\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x=\sqrt{2}\\x=-\sqrt{2}< 0\left(l\right)\\x=-\sqrt{\sqrt{19}-1}\\x=\sqrt{\sqrt{19}-1}>0\left(l\right)\end{matrix}\right.\)

19 tháng 8 2019

\(1+\sqrt{x^2-4x+3}-x=0\)

\(ĐK:\left\{{}\begin{matrix}\sqrt{x^2-4x+3\ge0}\\x-1\ge0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=1\\x\ge3\end{matrix}\right.\)

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

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

\(\Leftrightarrow2-2x=0\Rightarrow x=1\left(tm\right)\)

1 tháng 10 2019

a, ĐK:\(x^2-4x+3\ge0\Rightarrow\left[{}\begin{matrix}x\le1\\3\le x\end{matrix}\right.\)

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

Với x = 0 \(\Rightarrow pttm\)

Với \(x\ne0\) \(\Rightarrow\sqrt{x^2-4x+3}=x+1\)

\(\Rightarrow\left\{{}\begin{matrix}x\ge-1\\x^2-4x+3=x^2+2x+1\end{matrix}\right.\)\(\Rightarrow x=\frac{1}{3}\left(tm\right)\)

1 tháng 10 2019

b,ĐK: \(-\sqrt{10}\le x\le\sqrt{10}\)

\(PT\Leftrightarrow\left(x-3\right)\left(x+4\right)-\left(x-3\right)\sqrt{10-x^2}=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=3\left(tm\right)\\x+4-\sqrt{10-x^2}=0\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x=3\\x+4=\sqrt{10-x^2}\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=3\\x^2+8x+16=10-x^2\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=3\\x^2+4x+3=0\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=3\\\left[{}\begin{matrix}x=-1\\x=-3\end{matrix}\right.\end{matrix}\right.\)(tm)

NV
22 tháng 10 2019

a/ \(\Leftrightarrow x^2+5x-2-2\sqrt[3]{x^2+5x-2}+4=0\)

Đặt \(\sqrt[3]{x^2+5x-2}=a\)

\(a^3-2a+4=0\)

\(\Leftrightarrow\left(a+2\right)\left(a^2-2a+2\right)=0\Rightarrow a=-2\)

\(\Rightarrow\sqrt[3]{x^2+5x-2}=-2\Rightarrow x^2+5x+6=0\Rightarrow...\)

b/ ĐKXĐ:...

\(\Leftrightarrow-3\left(-x^2+4x+10\right)-5\sqrt{-x^2+4x+10}+42=0\)

Đặt \(\sqrt{-x^2+4x+10}=a\ge0\)

\(-3a^2-5a+42=0\Rightarrow\left[{}\begin{matrix}a=3\\a=-\frac{14}{3}\left(l\right)\end{matrix}\right.\)

\(\Rightarrow\sqrt{x^2+4x+10}=3\Rightarrow x^2-4x-1=0\Rightarrow...\)

NV
22 tháng 10 2019

c/ ĐKXĐ: ...

\(\Leftrightarrow x^2+3x+3\sqrt{x^2+3x}-10=0\)

Đặt \(\sqrt{x^2+3x}=a\ge0\)

\(a^2+3a-10=0\Rightarrow\left[{}\begin{matrix}a=2\\a=-5\left(l\right)\end{matrix}\right.\)

\(\Rightarrow\sqrt{x^2+3x}=2\Rightarrow x^2+3x-4=0\)

d/ ĐKXĐ: \(-1\le x\le2\)

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

\(\Leftrightarrow3-x+x^2=3+x-x^2+2\sqrt{2+x-x^2}\)

\(\Leftrightarrow2+x-x^2+\sqrt{2+x-x^2}-2=0\)

Đặt \(\sqrt{2+x-x^2}=a\ge0\)

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

\(\Rightarrow\sqrt{2+x-x^2}=1\Leftrightarrow x^2-x-1=0\)

e/ \(\Leftrightarrow\sqrt{x^2-3x+3}-1+\sqrt{x^2-3x+6}-2=0\)

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

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

\(\Leftrightarrow x^2-3x+2=0\)

30 tháng 3 2016

1) ĐK:x\(\ge\frac{1}{2}\)

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

\(\Leftrightarrow\begin{cases}x\ge0\\2x-1=x^2\end{cases}\)

\(\Leftrightarrow\begin{cases}x\ge0\\x=1\end{cases}\)

\(\Leftrightarrow x=1\)   (thỏa mãn)

30 tháng 3 2016

\(A=\frac{\left(3+\sqrt{5}\right)^2+\left(3-\sqrt{5}\right)^2}{\left(3+\sqrt{5}\right)\left(3+\sqrt{5}\right)}\)

\(A=\frac{18+10}{4}\)

\(A=7\)