giai p.t : \(\sqrt[3]{1-x}+\sqrt[3]{1+x}=1\)
giai p.t :\(\sqrt{\frac{x^3+1}{x+3}}+\sqrt{x+1}=\sqrt{x^2-x+1}+\sqrt{x+3}\)
ĐK: \(x\ge-1\)
\(\frac{pt\Leftrightarrow\sqrt{x+1}\sqrt{x^2-x+1}}{\sqrt{x+3}}+\sqrt{x+1}=\sqrt{x^2-x+1}+\sqrt{x+3}\)
\(\Leftrightarrow\frac{\sqrt{x+1}}{\sqrt{x+3}}\left(\sqrt{x^2-x+1}+\sqrt{x+3}\right)=\sqrt{x^2-x+1}+\sqrt{x+3}\)
\(\Leftrightarrow\frac{\sqrt{x+1}}{\sqrt{x+3}}=1\text{ (do }\sqrt{x^2-x+1}>0\text{)}\)
\(\Leftrightarrow...\)
giai p.t : \(x\sqrt{x^2-x+1}+4\sqrt{3x+1}=x^2+x+3\)
giai p.t : \(\sqrt{x+1}-\sqrt{x-7}=\sqrt{12-x}\)
giai p.t \(\frac{36}{\sqrt{x-2}}+\frac{4}{\sqrt{y-1}}=28-4\sqrt{x-2}-\sqrt{y-1}\)
ĐKXĐ: \(x>2;y>1\)
Khi đó Pt \(\Leftrightarrow\)\(\frac{36}{\sqrt{x-2}}+4\sqrt{x-2}+\frac{4}{\sqrt{y-1}}+\sqrt{y-1}=28\)
theo BĐT Cô si ta có \(\frac{36}{\sqrt{x-2}}+4\sqrt{x-2}\ge2.\sqrt{\frac{36}{\sqrt{x-2}}.4\sqrt{x-2}=24}\)
và \(\frac{4}{\sqrt{y-1}}+\sqrt{y-1}\ge2\sqrt{\frac{4}{\sqrt{y-1}}.\sqrt{y-1}}=4\)
Pt đã cho có VT>= 28 Dấu "=" xảy ra \(\Leftrightarrow\)
\(\frac{36}{\sqrt{x-2}}=4\sqrt{x-2}\Leftrightarrow x=11\)
và \(\frac{4}{\sqrt{y-1}}=\sqrt{y-1}\Leftrightarrow y=5\)
Đối chiếu với ĐK thì x=11; y=5 là nghiệm của PT
Ê Thắng tưởng off dòi mờ...nhanh thế....
giai p.t :\(\sqrt{x}+2\sqrt{x+3}=x+4\)
\(VT=1.\sqrt{x}+2.\sqrt{x+3}\le\frac{x+1}{2}+\frac{2^2+x+3}{2}=x+4=VP\)
giai p.t : \(\frac{1}{x}+\frac{1}{\sqrt{2-x^2}}=2\)
ĐK: \(x\ne0;\pm\sqrt{2}\)
Đặt \(x=a;\text{ }\sqrt{2-x^2}=b\Rightarrow a^2+b^2=2\text{ (1)}\)
pt đã cho: \(\frac{1}{a}+\frac{1}{b}=2\Leftrightarrow a+b=2ab\)
\(\left(1\right)\Leftrightarrow\left(a+b\right)^2-2ab=2\Leftrightarrow\left(a+b\right)^2-\left(a+b\right)-2=0\)
\(\Leftrightarrow a+b=-1\text{ hoặc }a+b=2\)
\(+TH1:\text{ }a+b=-1\Rightarrow x+\sqrt{2-x^2}=-1\Leftrightarrow\sqrt{2-x^2}=-x-1\)
\(\Rightarrow2-x^2=\left(-x-1\right)^2\Leftrightarrow2x^2+2x-1=0\)
\(\Leftrightarrow x=\frac{-1\pm\sqrt{3}}{2}\)
\(TH2:\text{ }a+b=2\) tương tự
Do dùng khá nhiều phép suy ra nên phải thử lại các nghiệm trước khi kết luận.
giai p.t :\(\sqrt{2x^2+x+6}+\sqrt{x^2+x+2}=x+\frac{4}{x}\)
giai phuong trinh
\(\frac{1}{\sqrt{x}+\sqrt{x+1}}+\frac{1}{\sqrt{x+1}+\sqrt{x+2}}+\frac{1}{\sqrt{x+2}+\sqrt{x+3}}=1\)
\(DK:x\ge0\)
\(\Leftrightarrow\frac{\sqrt{x}-\sqrt{x+1}}{x-x-1}+\frac{\sqrt{x+1}-\sqrt{x+2}}{x+1-x-2}+\frac{\sqrt{x+2}-\sqrt{x+3}}{x+2-x-3}=1\)
\(\Leftrightarrow-\sqrt{x}+\sqrt{x+1}-\sqrt{x+1}+\sqrt{x+2}-\sqrt{x+2}+\sqrt{x+3}=1\)
\(\Leftrightarrow\sqrt{x+3}-\sqrt{x}=1\)
\(\Leftrightarrow\sqrt{x+3}=1+\sqrt{x}\)
\(\Leftrightarrow x+3=x+2\sqrt{x}+1\)
\(\Leftrightarrow x=1\)
Vay nghiem cua PT la \(x=1\)
giai phuong trinh :
\(\dfrac{\sqrt{x+3}+\sqrt{x-1}}{\sqrt{x+3}-\sqrt{x-1}}=\dfrac{13-x^2}{4}\)
\(\Leftrightarrow\dfrac{x+3+x-1+2\sqrt{\left(x+3\right)\left(x-1\right)}}{x+3-x+1}=\dfrac{13-x^2}{4}\)
\(\Leftrightarrow2x+2+2\sqrt{\left(x+3\right)\left(x-1\right)}=13-x^2\)
\(\Leftrightarrow\sqrt{4\left(x+3\right)\left(x-1\right)}=13-x^2-2x-2=-x^2-2x+11\)
=>\(x\simeq1,37\)