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Đặt \(\left(\sqrt{a};\sqrt{b};\sqrt{c}\right)\rightarrow\left(x;y;z\right)\)\(\Rightarrow\)\(x^2+y^2+z^2=4\)
\(P=\frac{x^3}{x+3y}+\frac{y^3}{y+3z}+\frac{z^3}{z+3x}=\frac{x^4}{x^2+3xy}+\frac{y^4}{y^2+3yz}+\frac{z^4}{z^2+3zx}\)
\(\ge\frac{\left(x^2+y^2+z^2\right)^2}{x^2+y^2+z^2+3\left(xy+yz+zx\right)}\ge\frac{\left(x^2+y^2+z^2\right)^2}{x^2+y^2+z^2+3\left(x^2+y^2+z^2\right)}=\frac{4^2}{4+3.4}=1\)
Dấu "=" xảy ra \(\Leftrightarrow\)\(a=b=c=\frac{2}{\sqrt{3}}\)
\(A=\left(\dfrac{x+2}{x\sqrt{x}-1}+\dfrac{\sqrt{x}}{x+\sqrt{x}+1}+\dfrac{1}{1-\sqrt{x}}\right):\dfrac{\sqrt{x}-1}{2}\left(đk:x\ge0,x\ne1\right)\)
\(=\dfrac{x+2+\sqrt{x}\left(\sqrt{x}-1\right)-\left(x+\sqrt{x}+1\right)}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}.\dfrac{2}{\sqrt{x}-1}\)
\(=\dfrac{x-2\sqrt{x}+1}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}.\dfrac{2}{\sqrt{x}-1}\)
\(=\dfrac{\left(\sqrt{x}-1\right)^2.2}{\left(\sqrt{x}-1\right)^2\left(x+\sqrt{x}+1\right)}=\dfrac{2}{x+\sqrt{x}+1}\)
Để A nguyên thì: \(x+\sqrt{x}+1\inƯ\left(2\right)=\left\{-2;-1;1;2\right\}\)
Mà \(x+\sqrt{x}+1=\left(x+\sqrt{x}+\dfrac{1}{4}\right)+\dfrac{3}{4}=\left(\sqrt{x}+\dfrac{1}{2}\right)^2+\dfrac{3}{4}\ge\dfrac{3}{4}>0\)
\(\Rightarrow x+\sqrt{x}+1\in\left\{1;2\right\}\)
+ Với \(x+\sqrt{x}+1=1\)
\(\Leftrightarrow\sqrt[]{x}\left(\sqrt{x}+1\right)=0\)
\(\Leftrightarrow x=0\left(tm\right)\left(do.\sqrt{x}+1\ge1>0\right)\)
+ Với \(x+\sqrt{x}+1=2\)
\(\Leftrightarrow\left(x+\sqrt{x}+\dfrac{1}{4}\right)=\dfrac{5}{4}\)
\(\Leftrightarrow\left(\sqrt{x}+\dfrac{1}{2}\right)^2=\dfrac{5}{4}\)
\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}+\dfrac{1}{2}=\dfrac{\sqrt{5}}{2}\\\sqrt{x}+\dfrac{1}{2}=-\dfrac{\sqrt{5}}{2}\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}=\dfrac{\sqrt{5}-1}{2}\\\sqrt{x}=-\dfrac{\sqrt{5}+1}{2}\left(VLý\right)\end{matrix}\right.\)
\(\Leftrightarrow x=\dfrac{3-\sqrt{5}}{2}\left(tm\right)\)
Vậy \(S=\left\{1;\dfrac{3-\sqrt{5}}{2}\right\}\)
1. Ta có: \(x^2-2xy-x+y+3=0\)
<=> \(x^2-2xy-2.x.\frac{1}{2}+2.y.\frac{1}{2}+\frac{1}{4}+y^2-y^2-\frac{1}{4}+3=0\)
<=> \(\left(x-y-\frac{1}{2}\right)^2-y^2=-\frac{11}{4}\)
<=> \(\left(x-2y-\frac{1}{2}\right)\left(x-\frac{1}{2}\right)=-\frac{11}{4}\)
<=> \(\left(2x-4y-1\right)\left(2x-1\right)=-11\)
Th1: \(\hept{\begin{cases}2x-4y-1=11\\2x-1=-1\end{cases}}\Leftrightarrow\hept{\begin{cases}x=0\\y=-3\end{cases}}\)
Th2: \(\hept{\begin{cases}2x-4y-1=-11\\2x-1=1\end{cases}}\Leftrightarrow\hept{\begin{cases}x=1\\y=3\end{cases}}\)
Th3: \(\hept{\begin{cases}2x-4y-1=1\\2x-1=-11\end{cases}}\Leftrightarrow\hept{\begin{cases}x=-5\\y=-3\end{cases}}\)
Th4: \(\hept{\begin{cases}2x-4y-1=-1\\2x-1=11\end{cases}}\Leftrightarrow\hept{\begin{cases}x=6\\y=3\end{cases}}\)
Kết luận:...
Δ=(2m-2)^2-4(2m-5)
=4m^2-8m+4-8m+20
=4m^2-16m+24
=4m^2-16m+16+8=(2m-4)^2+8>=8>0 với mọi m
=>Phương trình luôn có hai nghiệm phân biệt
\(B=\dfrac{x_1^2}{x^2_2}+\dfrac{x_2^2}{x_1^2}\)
\(=\dfrac{x_1^4+x_2^4}{\left(x_1\cdot x_2\right)^2}=\dfrac{\left(x_1^2+x_2^2\right)^2-2\left(x_1\cdot x_2\right)^2}{\left(x_1\cdot x_2\right)^2}\)
\(=\dfrac{\left[\left(2m-2\right)^2-2\left(2m-5\right)\right]^2-2\left(2m-5\right)^2}{\left(2m-5\right)^2}\)
\(=\dfrac{\left(4m^2-8m+4-4m+10\right)^2}{\left(2m-5\right)^2}-2\)
\(=\left(\dfrac{4m^2-12m+14}{2m-5}\right)^2-2\)
\(=\left(\dfrac{4m^2-10m-2m+5+9}{2m-5}\right)^2-2\)
\(=\left(2m-1+\dfrac{9}{2m-5}\right)^2-2\)
Để B nguyên thì \(2m-5\in\left\{1;-1;3;-3;9;-9\right\}\)
=>\(m\in\left\{3;2;4;1;7\right\}\)
a. ĐK: \(x\ge0,x\ne49\)
\(M=\frac{3\left(\sqrt{x}+7\right)-\left(\sqrt{x}-7\right)}{\left(\sqrt{x}-7\right)\left(\sqrt{x}+7\right)}:\frac{2\sqrt{x}+6}{x-49}\)
\(=\frac{2\sqrt{x}+28}{x-49}.\frac{x-49}{2\sqrt{x}+6}=\frac{2\sqrt{x}+28}{2\sqrt{x}+6}\)
b. M nguyên \(\Leftrightarrow\frac{2\sqrt{x}+28}{2\sqrt{x}+6}\in Z\Rightarrow\frac{2\sqrt{x}+6+22}{2\sqrt{x}+6}\in Z\Rightarrow1+\frac{22}{2\sqrt{x}+6}\in Z\Rightarrow\frac{22}{2\sqrt{x}+6}\in Z\Rightarrow\left(2\sqrt{x}+6\right)\inƯ\left(22\right)\)
Đến đây đã rất dễ dàng rồi nhé ^^
đề không cho tìm x NGUYÊN để m nguyên mà chỉ tìm các điểm x để m nguyên thôi
\(P=\frac{4\sqrt{x}+3}{x+\sqrt{x}}+\frac{\sqrt{x}}{\sqrt{x}+1}\)
\(P=\frac{4\sqrt{x}+3}{\sqrt{x}\left(\sqrt{x}+1\right)}+\frac{\sqrt{x}}{\sqrt{x}+1}=\frac{4\sqrt{x}+3}{\sqrt{x}\left(\sqrt{x}+1\right)}+\frac{x}{\sqrt{x}\left(\sqrt{x}+1\right)}\)
\(=\frac{x+4\sqrt{x}+3}{\sqrt{x}\left(\sqrt{x}+1\right)}\inℤ\Leftrightarrow x+4\sqrt{x}+3⋮\sqrt{x}\)
Giải tiếp nhé sau đó thử chọn :V
\(p=\frac{4\sqrt{x}+3}{x+\sqrt{x}}+\frac{\sqrt{x}}{\sqrt{x}+1}\)
\(=\frac{4\sqrt{x}+3}{\sqrt{x}\left(\sqrt{x}+1\right)}+\frac{x}{\sqrt{x}\left(\sqrt{x}+1\right)}\)
\(=\frac{x+\sqrt{x}+3\sqrt{x}+3}{\sqrt{x}\left(\sqrt{x}+1\right)}=\frac{\left(\sqrt{x}+3\right)\left(\sqrt{x}+1\right)}{\sqrt{x}\left(\sqrt{x}+1\right)}\)
\(=\frac{\sqrt{x}+3}{\sqrt{x}}=1+\frac{3}{\sqrt{x}}\)
Để \(x\in Z\Rightarrow P\in Z\)
\(\Rightarrow\sqrt{x}\inƯ\left(3\right)= \left\{-3;3\right\}\)
\(\Leftrightarrow x=9\left(t.mĐKXĐ\right)\)
Quanda hả bạn