Tìm GTNN của:
\(P=\dfrac{x^2-2x+3}{x^2}\left(x\ne0\right)\)
K
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Những câu hỏi liên quan
15 tháng 3 2021
a) Ta có: \(P=\left(\dfrac{x^2-2x}{2x^2+8}-\dfrac{2x^2}{8-4x+2x^2-x^3}\right)\left(1-\dfrac{1}{x}-\dfrac{2}{x^2}\right)\)
\(=\left(\dfrac{x^2-2x}{2\left(x^2+4\right)}-\dfrac{2x^2}{4\left(2-x\right)+x^2\left(2-x\right)}\right)\left(1-\dfrac{1}{x}-\dfrac{2}{x^2}\right)\)
\(=\left(\dfrac{x^2-2x}{2\left(x^2+4\right)}-\dfrac{2x^2}{\left(2-x\right)\left(x^2+4\right)}\right)\left(1-\dfrac{1}{x}-\dfrac{2}{x^2}\right)\)
\(=\left(\dfrac{\left(x^2-2x\right)\left(x-2\right)}{2\left(x-2\right)\left(x^2+4\right)}+\dfrac{4x^2}{2\left(x-2\right)\left(x^2+4\right)}\right)\cdot\left(1-\dfrac{1}{x}-\dfrac{2}{x^2}\right)\)
\(=\dfrac{x^3-x^2-2x^2+4x+4x^2}{2\left(x-2\right)\left(x^2+4\right)}\cdot\left(1-\dfrac{1}{x}-\dfrac{2}{x^2}\right)\)
\(=\dfrac{x^3+x^2+4x}{2\left(x-2\right)\left(x^2+4\right)}\cdot\dfrac{x^2-x-2}{x^2}\)
\(=\dfrac{x\left(x^2+x+4\right)}{2\left(x-2\right)\left(x^2+4\right)}\cdot\dfrac{\left(x-2\right)\left(x+1\right)}{x^2}\)
\(=\dfrac{\left(x^2+x+4\right)\left(x+1\right)}{2x\left(x^2+4\right)}\)
1 tháng 5 2022
ĐKXĐ: \(x\ne\pm1;x\ne0\)
a)\(\left(\dfrac{x+1}{x-1}-\dfrac{x-1}{x+1}\right):\dfrac{2x}{5x-5}-\dfrac{x^2-1}{x^2+2x+1}\)
\(=\left(\dfrac{\left(x+1\right)^2}{\left(x-1\right)\left(x+1\right)}-\dfrac{\left(x-1\right)^2}{\left(x-1\right)\left(x+1\right)}\right):\dfrac{2x}{5x-5}-\dfrac{x^2-1}{x^2+2x+1}\)
\(=\dfrac{x^2+2x+1-\left(x^2-2x+1\right)}{\left(x-1\right)\left(x+1\right)}:\dfrac{2x}{5x-5}-\dfrac{x^2-1}{x^2+2x+1}\)
\(=\dfrac{4x}{\left(x-1\right)\left(x+1\right)}:\dfrac{2x}{5x-5}-\dfrac{x^2-1}{x^2+2x+1}\)
\(=\dfrac{4x}{\left(x-1\right)\left(x+1\right)}.\dfrac{5\left(x-1\right)}{2x}-\dfrac{x^2-1}{x^2+2x+1}\)
\(=\dfrac{10}{x+1}-\dfrac{\left(x+1\right)\left(x-1\right)}{\left(x+1\right)^2}\)
\(=\dfrac{10}{x+1}-\dfrac{x-1}{x+1}\)
\(=\dfrac{11-x}{x+1}\)
b) \(A=\dfrac{11-x}{x+1}=2\)
\(\Leftrightarrow11-x=2\left(x+1\right)\)
\(\Leftrightarrow11-x=2x+2\)
\(\Leftrightarrow-x-2x=2-11\)
\(\Leftrightarrow-3x=-9\)
\(\Leftrightarrow x=3\left(nhận\right)\)
c) -Để \(A=\dfrac{11-x}{x+1}\in Z\) thì:
\(\left(11-x\right)⋮\left(x+1\right)\)
\(\Rightarrow\left(12-x-1\right)⋮\left(x+1\right)\)
\(\Rightarrow12⋮\left(x+1\right)\)
\(\Rightarrow\left(x+1\right)\inƯ\left(12\right)\)
\(\Rightarrow\left(x+1\right)\in\left\{1;2;3;4;6;12;-1;-2;-3;-4;-6;-12\right\}\)
\(\Rightarrow x\in\left\{2;3;5;11;-2;-3;-4;-5;-7;-13\right\}\)
N
6 tháng 5 2023
\(\left(2x^2-\dfrac{1}{x^2}\right)^4=C^k_4\left(2x^2\right)^{4-k}\left(-\dfrac{1}{x^2}\right)^k\)
\(=C^k_4.2^{4-k}.x^{8-2k-2k}.\left(-1\right)^k\)
\(=C^k_4.2^{4-k}.x^{8-4k}.\left(-1\right)^k\)
\(ycbt\Leftrightarrow8-4k=0\Leftrightarrow k=2\)
\(\Rightarrow C^2_4.2^{4-2}.\left(-1\right)^2=24\)
Vậy số hạng không chứa \(x\) trong khai triển là \(24\).
NV
Nguyễn Việt Lâm
Giáo viên
26 tháng 8 2021
\(P\ge\dfrac{1}{2}\left(\dfrac{1}{x-2}+\dfrac{1}{3-x}\right)^2+\dfrac{4}{\left(x-2+3-x\right)^2}=\dfrac{1}{2}\left(\dfrac{1}{x-2}+\dfrac{1}{3-x}\right)^2+4\)
\(P\ge\dfrac{1}{2}\left(\dfrac{4}{x-4+3-x}\right)^2+4=12\)
Dấu "=" xảy ra khi \(x-2=3-x\Rightarrow x=\dfrac{5}{2}\)
24 tháng 1 2021
ĐKXĐ: \(x\notin\left\{-1;-\dfrac{1}{2}\right\}\)
a) Ta có: \(P=\left(\dfrac{2x}{x^3+x^2+x+1}+\dfrac{1}{x+1}\right):\left(1+\dfrac{x}{x+1}\right)\)
\(=\left(\dfrac{2x}{\left(x+1\right)\left(x^2+1\right)}+\dfrac{x^2+1}{\left(x^2+1\right)\left(x+1\right)}\right):\left(\dfrac{x+1+x}{x+1}\right)\)
\(=\dfrac{x^2+2x+1}{\left(x+1\right)\left(x^2+1\right)}:\dfrac{2x+1}{x+1}\)
\(=\dfrac{\left(x+1\right)^2}{\left(x+1\right)\left(x^2+1\right)}\cdot\dfrac{x+1}{2x+1}\)
\(=\dfrac{x^2+2x+1}{\left(2x+1\right)\left(x^2+1\right)}\)
b) Vì \(x=\dfrac{1}{4}\) thỏa mãn ĐKXĐ
nên Thay \(x=\dfrac{1}{4}\) vào biểu thức \(P=\dfrac{x^2+2x+1}{\left(2x+1\right)\left(x^2+1\right)}\), ta được:
\(P=\left[\left(\dfrac{1}{4}\right)^2+2\cdot\dfrac{1}{4}+1\right]:\left[\left(2\cdot\dfrac{1}{4}+1\right)\left(\dfrac{1}{16}+1\right)\right]\)
\(=\left(\dfrac{1}{16}+\dfrac{1}{2}+1\right):\left[\left(\dfrac{1}{2}+1\right)\left(\dfrac{1}{16}+1\right)\right]\)
\(=\dfrac{25}{16}:\dfrac{51}{32}=\dfrac{25}{16}\cdot\dfrac{32}{51}=\dfrac{50}{51}\)
Vậy: Khi \(x=\dfrac{1}{4}\) thì \(P=\dfrac{50}{51}\)
ND
Nguyễn Đức Trí
VIP
30 tháng 8 2023
\(B=-\left(\dfrac{4}{9}x-\dfrac{2}{15}\right)^6+3\)
vì \(B=-\left(\dfrac{4}{9}x-\dfrac{2}{15}\right)^6\le0,\forall x\inℝ\)
\(\Rightarrow B=-\left(\dfrac{4}{9}x-\dfrac{2}{15}\right)^6+3\le3\)
Dấu "=" xảy ra khi và chỉ khi
\(\dfrac{4}{9}x-\dfrac{2}{15}=0\Rightarrow\dfrac{4}{9}x=\dfrac{2}{15}\Rightarrow x=\dfrac{9}{15}\)
Vậy \(GTLN\left(B\right)=3\left(tạix=\dfrac{9}{15}\right)\)
ND
Nguyễn Đức Trí
VIP
30 tháng 8 2023
\(A=\left(2x+\dfrac{1}{3}\right)^4-1\)
vì \(\left(2x+\dfrac{1}{3}\right)^4\ge0,\forall x\inℝ\)
\(\Rightarrow A=\left(2x+\dfrac{1}{3}\right)^4-1\ge-1\)
Dấu "=" xảy ra khi và chỉ khi
\(2x+\dfrac{1}{3}=0\Rightarrow2x=-\dfrac{1}{3}\Rightarrow x=-\dfrac{1}{6}\)
\(\Rightarrow GTNN\left(A\right)=-1\left(tạix=-\dfrac{1}{6}\right)\)
17 tháng 12 2022
C=|2x-3/5|+4/3>=4/3
Dấu = xảy ra khi x=3/10
D=|x-3|+|-x-2|>=|x-3-x-2|=5
Dấu = xảy ra khi -2<=x<=3
NV
Nguyễn Việt Lâm
Giáo viên
1 tháng 8 2021
\(y=x+\dfrac{1}{x}-5\ge2\sqrt{\dfrac{x}{x}}-5=-3\)
\(y_{min}=-3\) khi \(x=1\)
\(y=4x^2+\dfrac{1}{2x}+\dfrac{1}{2x}-4\ge3\sqrt[3]{\dfrac{4x^2}{2x.2x}}-4=-1\)
\(y_{min}=-1\) khi \(x=\dfrac{1}{2}\)
\(y=x+\dfrac{4}{x}\Rightarrow y'=1-\dfrac{4}{x^2}=0\Rightarrow x=-2\)
\(y\left(-2\right)=-4\Rightarrow\max\limits_{x>0}y=-4\) khi \(x=-2\)
NV
Nguyễn Việt Lâm
Giáo viên
20 tháng 3 2022
ĐKXĐ: \(x\ge-2;x\ne-1\)
\(M=\dfrac{x^2-2x}{x^3+1}+\dfrac{1}{2}\left(\dfrac{1-\sqrt{x+2}+1+\sqrt{x+2}}{1-\left(x+2\right)}\right)\)
\(=\dfrac{x^2-2x}{\left(x+1\right)\left(x^2-x+1\right)}-\dfrac{1}{x+1}=\dfrac{x^2-2x-\left(x^2-x+1\right)}{\left(x+1\right)\left(x^2-x+1\right)}\)
\(=\dfrac{-\left(x+1\right)}{\left(x+1\right)\left(x^2-x+1\right)}=-\dfrac{1}{x^2-x+1}\)
\(M=-\dfrac{1}{\left(x-\dfrac{1}{2}\right)^2+\dfrac{3}{4}}\ge-\dfrac{1}{\dfrac{3}{4}}=-\dfrac{4}{3}\)
\(M_{min}=-\dfrac{4}{3}\) khi \(x=\dfrac{1}{2}\)
\(P-\dfrac{2}{3}=\dfrac{x^2-6x+9}{3x^2}=\dfrac{\left(x-3\right)^2}{3x^2}\ge0\Rightarrow P\ge\dfrac{2}{3}\).
Dấu "=" xảy ra khi x = 3.