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a) Để biểu thức được xác định thì \(\left\{{}\begin{matrix}x+2\ge0\\5-x\le0\end{matrix}\right.\)\(\Leftrightarrow\)\(\left\{{}\begin{matrix}x\ge-2\\x\le5\end{matrix}\right.\)\(\Leftrightarrow-2\le x\le5\)
Vậy điều kiện xác định của biểu thức là \(-2\le x\le5\)
b) \(\sqrt{4x^2-16x+16}=6\Leftrightarrow\sqrt{\left(2x\right)^2-2.2x.4+4^2}=6\Leftrightarrow\sqrt{\left(2x-4\right)^2}=6\Leftrightarrow\left|2x-4\right|=6\Leftrightarrow\left|x-2\right|=3\)(1)
TH1: x\(\ge2\) thì (1)\(\Leftrightarrow x-2=3\Leftrightarrow x=5\left(tm\right)\)
TH2: \(x< 2\Leftrightarrow2-x=3\Leftrightarrow x=-1\left(tm\right)\)
Vậy S={-1;5}
ĐKXĐ: \(\left\{{}\begin{matrix}x+2\ge0\\5-x\ge0\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}x\ge-2\\x\le5\end{matrix}\right.\) \(\Rightarrow-2\le x\le5\)
b/ \(\sqrt{4x^2-16x+16}=6\)
\(\Leftrightarrow\sqrt{\left(2x-4\right)^2}=6\)
\(\Leftrightarrow\left|2x-4\right|=6\)
\(\Leftrightarrow\left[{}\begin{matrix}2x-4=6\\2x-4=-6\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}2x=10\\2x=-2\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x=5\\x=-1\end{matrix}\right.\)
\(a,\sqrt{x+1}=\sqrt{2-x}\)
\(\Rightarrow x+1=2-x\)
\(\Rightarrow2x=1\)
\(\Rightarrow x=\frac{1}{2}\)
a) \(ĐKXĐ:-1\le x\le2\)
Bình phương 2 vế ta có:
\(x+1=2-x\)\(\Leftrightarrow2x=1\)\(\Leftrightarrow x=\frac{1}{2}\)( đpcm )
Vậy \(x=\frac{1}{2}\)
b) \(ĐKXĐ:x\ge1\)
\(\sqrt{36x-36}-\sqrt{9x-9}-\sqrt{4x-4}=16-\sqrt{x-1}\)
\(\Leftrightarrow\sqrt{36\left(x-1\right)}-\sqrt{9\left(x-1\right)}-\sqrt{4\left(x-1\right)}+\sqrt{x-1}=16\)
\(\Leftrightarrow6\sqrt{x-1}-3\sqrt{x-1}-2\sqrt{x-1}+\sqrt{x-1}=16\)
\(\Leftrightarrow2\sqrt{x-1}=16\)\(\Leftrightarrow\sqrt{x-1}=8\)
\(\Leftrightarrow x-1=64\)\(\Leftrightarrow x=65\)( thỏa mãn ĐKXĐ )
Vậy \(x=65\)
c) \(ĐKXĐ:x\ge1\)
\(\sqrt{16x-16}-\sqrt{9x-9}+\sqrt{4x-4}+\sqrt{x-1}=8\)
\(\Leftrightarrow\sqrt{16\left(x-1\right)}-\sqrt{9\left(x-1\right)}+\sqrt{4\left(x-1\right)}+\sqrt{x-1}=8\)
\(\Leftrightarrow4\sqrt{x-1}-3\sqrt{x-1}+2\sqrt{x-1}+\sqrt{x-1}=8\)
\(\Leftrightarrow4\sqrt{x-1}=8\)\(\Leftrightarrow\sqrt{x-1}=2\)
\(\Leftrightarrow x-1=4\)\(\Leftrightarrow x=5\)( thỏa mãn ĐKXĐ )
Vậy \(x=5\)
1) a) \(\hept{\begin{cases}2x-y=5\\x+y=4\end{cases}}\)<=> \(\hept{\begin{cases}3x=9\\x+y=4\end{cases}}\)<=>\(\hept{\begin{cases}x=3\\3+y=4\end{cases}}\)<=> \(\hept{\begin{cases}x=3\\y=1\end{cases}}\)
\(16x^5-8x^3+x=0\)(1) <=> \(x\left(16x^4-8x^2+1\right)=0\)
<=> \(x_1=0\)hoac \(16x^4-8x^2+1=0\)
\(16x^4-8x^2+1=0\)
Dat \(x^2=t\left(t\ge0\right)\)phuong trinh tro thanh
\(16x^2-8x+1=0\)
\(\left(a=16;b'=\frac{b}{2}=-\frac{8}{2}=-4:c=1\right)\)
\(\Delta'=b'^2-ac=\left(-4\right)^2-16\cdot1=16-16=0\)
Phuong trinh co nghiem kep t1 =t2=\(-\frac{b'}{a}=-\frac{-4}{1}=4\)(thoa)
Voi t=4 ta duoc
\(x^2=4\)<=> \(x_2=2,x_3=-2\)
Vay nghiem cua phuong trinh (1) la \(x_1=0,x_2=2,x_3=-2\)
a)\(\)https://www.cymath.com/answer?q=2sqrt(27)-6sqrt(4%2F3)%2B3%2F5sqrt(75)
\(M=2\sqrt{27}-6\sqrt{\frac{4}{3}}+\frac{3}{5}\sqrt{75}=2\sqrt{3^2.3}-6\sqrt{\frac{2^2.3}{3^2}}+\frac{3}{5}\sqrt{5^2.3}=.\)
\(=6\sqrt{3}-4\sqrt{3}+3\sqrt{3}=5\sqrt{3}\)
\(P=\frac{2}{x-1}\sqrt{\frac{x^2-2x+1}{4x^2}}.Với...0< x< 1\Leftrightarrow\) \(P=\frac{2}{x-1}\sqrt{\frac{\left(x-1\right)^2}{\left(2x\right)^2}}=\frac{2}{(x-1)}.\frac{\left(1-x\right)}{2x}=\frac{-1}{x}.\)
1/ \(\frac{3}{2}x^2+y^2+z^2+yz=1\Leftrightarrow3x^2+2y^2+2z^2+2yz=2\)
\(\Leftrightarrow\left(x^2+y^2+z^2+2xy+2yz+2zx\right)+\left(x^2-2xy+y^2\right)+\left(x^2-2zx+z^2\right)=2\)
\(\Leftrightarrow\left(x+y+z\right)^2+\left(x-y\right)^2+\left(x-z\right)^2=2\)
\(\Rightarrow-\sqrt{2}\le x+y+z\le\sqrt{2}\)
Suy ra MIN A = \(-\sqrt{2}\)khi \(x=y=z=-\frac{\sqrt{2}}{3}\)
Mấy bài này dài vật vã ghê =)))))))))))))
1, a, \(\frac{3+4\sqrt{3}}{\sqrt{6}+\sqrt{2}-\sqrt{5}}\)
= \(\frac{\left(3+4\sqrt{3}\right)\left(\sqrt{6}+\sqrt{2}+\sqrt{5}\right)}{\left(\sqrt{6}+\sqrt{2}-\sqrt{5}\right)\left(\sqrt{6}+\sqrt{2}+\sqrt{5}\right)}\)
=\(\frac{\left(3+4\sqrt{3}\right)\left(\sqrt{6}+\sqrt{2}+\sqrt{5}\right)}{\left(\sqrt{6}+\sqrt{2}\right)^2-5}\)
=\(\frac{\left(3+4\sqrt{3}\right)\left(\sqrt{6}+\sqrt{2}+\sqrt{5}\right)}{8+4\sqrt{3}-5}\)
= \(\frac{\left(3+4\sqrt{3}\right)\left(\sqrt{6}+\sqrt{2}+\sqrt{5}\right)}{3+4\sqrt{3}}\)
=\(\sqrt{6}+\sqrt{2}+\sqrt{5}\)
b, M = \(\frac{\sqrt{3}\left(x-1\right)}{\sqrt{x^2}-x+1}\)(ĐKXĐ: \(x\ge0\))
= \(\frac{\sqrt{3}\left(x-1\right)}{x-x+1}\)
= \(\sqrt{3}\left(x-1\right)\)
Thay x = \(2+\sqrt{3}\)(TMĐK) vào M ta có:
M = \(\sqrt{3}\left(2+\sqrt{3}-1\right)=\sqrt{3}\left(1+\sqrt{3}\right)=3+\sqrt{3}\)
Vậy với x = \(2+\sqrt{3}\)thì M = \(3+\sqrt{3}\)
2, Mình chỉ giải câu a thôi nhé:
\(\sqrt{1+b}+\sqrt{1+c}\ge2\sqrt{1+a}\)
\(\Leftrightarrow\left(\sqrt{1+b}+\sqrt{1+c}\right)^2\ge\left(2\sqrt{1+a}\right)^2\)
\(\Leftrightarrow1+b+2\sqrt{\left(1+b\right)\left(1+c\right)}+1+c\ge4\left(1+a\right)\)
\(\Leftrightarrow2+b+c+2\sqrt{\left(1+b\right)\left(1+c\right)}\ge4\left(1+a\right)\left(1\right)\)
Vì \(\left(\sqrt{1+b}-\sqrt{1+c}\right)^2\ge0\)
\(\Rightarrow2+b+c\ge2\sqrt{\left(1+b\right)\left(1+c\right)}\left(2\right)\)
Từ \(\left(1\right),\left(2\right)\Rightarrow4+2\left(b+c\right)+2\sqrt{\left(1+b\right)\left(1+c\right)}\ge4\left(1+a\right)+2\sqrt{\left(1+b\right)\left(1+c\right)}\)
\(\Leftrightarrow4+2\left(b+c\right)\ge4\left(1+a\right)\)
\(\Leftrightarrow4+2\left(b+c\right)\ge4+4a\)
\(\Leftrightarrow2\left(b+c\right)\ge4a\)
\(\Leftrightarrow b+c\ge2a\)
4*. Thật ra cái này mình xài làm trội, làm giảm là được mà
Đặt A = \(\frac{1}{\sqrt{2}}+\frac{1}{\sqrt{3}}+....+\frac{1}{\sqrt{n}}\)
\(\frac{1}{2}A=\frac{1}{2\sqrt{2}}+\frac{1}{2\sqrt{3}}+....+\frac{1}{2\sqrt{n}}\)
\(\frac{1}{2}A=\frac{1}{\sqrt{2}+\sqrt{2}}+\frac{1}{\sqrt{3}+\sqrt{3}}+....+\frac{1}{\sqrt{n}+\sqrt{n}}\)
Ta có: \(\frac{1}{\sqrt{2}+\sqrt{2}}>\frac{1}{\sqrt{3}+\sqrt{2}}\)
\(\frac{1}{\sqrt{3}+\sqrt{3}}>\frac{1}{\sqrt{4}+\sqrt{3}}\)
+ .........................................................
\(\frac{1}{\sqrt{n}+\sqrt{n}}>\frac{1}{\sqrt{n+1}+\sqrt{n}}\)
Cộng tất cả vào
\(\Rightarrow\frac{1}{\sqrt{2}+\sqrt{2}}+\frac{1}{\sqrt{3}+\sqrt{3}}+...+\frac{1}{\sqrt{n}+\sqrt{n}}>\frac{1}{\sqrt{3}+\sqrt{2}}+\frac{1}{\sqrt{4}+\sqrt{3}}+...+\frac{1}{\sqrt{n+1}+\sqrt{n}}\)\(\frac{1}{2}A>\frac{\sqrt{3}-\sqrt{2}}{3-2}+\frac{\sqrt{4}-\sqrt{3}}{4-3}+...+\frac{\sqrt{n+1}-\sqrt{n}}{n+1-n}\)
\(\frac{1}{2}A>\sqrt{3}-\sqrt{2}+\sqrt{4}-\sqrt{3}+...+\sqrt{n+1}-\sqrt{n}\)
\(\frac{1}{2}A>\sqrt{n+1}-\sqrt{2}\)
\(A>2\sqrt{n+1}-2\sqrt{2}>2\sqrt{n+1}-3\)
\(A+1>2\sqrt{n+1}-3+1\)
\(A+1>2\sqrt{n+1}-2\)
\(A+1>2\left(\sqrt{n+1}-1\right)\)
Vậy ta có điều phải chứng minh.
ĐKXĐ \(x+2\ne0\)và \(5-x\ne0\)
<=> \(x\ne-2\)và \(x\ne5\)
b)\(\sqrt{4x^2-16+16}=6\)<=> \(\sqrt{2^2\left(x^2-2\cdot x\cdot2+2^2\right)}=6\)<=> \(2\sqrt{\left(x-2\right)^2}=6\)<=> \(|x-2|=3\)
Với \(x-2>0\)<=> \(x>2\)
=> \(|x-2|=x-2\)
Phương trình trở thành \(x-2=3\)<=> \(x=5\)(thỏa)
Với \(x-2< 0\)<=> \(x< 2\)
=> \(|x-2|=-\left(x-2\right)=2-x\)
Phương trình trở thành \(2-x=3\)<=> \(-x=1\)<=> \(x=-1\)(thỏa)
Vậy nghiệm của phương trình là\(x=5\)và\(x=-1\)