TH1: \(n\) chẵn \(\Rightarrow n=2k\) (với \(k\in N\)^*)

\(p=\dfrac{2k\left(2k+1\right)}{2}-1=2k^2+k-1=\left(k+1\right)\left(2k-1\right)\)

Do \(k+1\ge2>1\) nên p nguyên tố khi và chỉ khi: \(\left\{{}\begin{matrix}2k-1=1\\k+1\text{ là số nguyên tố}\end{matrix}\right.\)

\(2k-1=1\Rightarrow k=1\)

Khi đó \(p=2\) (thỏa mãn)

TH2: \(n\) lẻ \(\Rightarrow n=2k+1\) (với \(k\in N\))

\(p=\dfrac{\left(2k+1\right)\left(2k+2\right)}{2}-1=\left(2k+1\right)\left(k+1\right)-1=2k^2+3k=k\left(2k+3\right)\)

Do \(2k+3\ge3>1\) nên p là nguyên tố khi và chỉ khi \(\left\{{}\begin{matrix}k=1\\2k+3\text{ là số nguyên tố}\end{matrix}\right.\)

Khi \(k=1\Rightarrow p=5\) là số nguyên tố (thỏa mãn)

Vậy \(p=\left\{2;5\right\}\)

Δ=(2m-2)^2-4(m-3)

=4m^2-8m+4-4m+12

=4m^2-12m+16

=4m^2-12m+9+7=(2m-3)^2+7>=7>0 với mọi m

=>Phương trình luôn có hai nghiệm phân biệt

\(\left(\dfrac{1}{x1}-\dfrac{1}{x2}\right)^2=\dfrac{\sqrt{11}}{2}\)

=>\(\dfrac{1}{x_1^2}+\dfrac{1}{x_2^2}-\dfrac{2}{x_1x_2}=\dfrac{\sqrt{11}}{2}\)

=>\(\dfrac{\left(\left(x_1+x_2\right)^2-2x_1x_2\right)}{\left(x_1\cdot x_2\right)^2}-\dfrac{2}{x_1\cdot x_2}=\dfrac{\sqrt{11}}{2}\)

=>\(\dfrac{\left(2m-2\right)^2-2\left(m-3\right)}{\left(-m+3\right)^2}-\dfrac{2}{-m+3}=\dfrac{\sqrt{11}}{2}\)

=>\(\dfrac{4m^2-8m+4-2m+6}{\left(m-3\right)^2}+\dfrac{2}{m-3}=\dfrac{\sqrt{11}}{2}\)

=>\(\dfrac{4m^2-10m+10+2m-6}{\left(m-3\right)^2}=\dfrac{\sqrt{11}}{2}\)

=>\(\sqrt{11}\left(m-3\right)^2=2\left(4m^2-8m+4\right)\)

=>\(\sqrt{11}\left(m-3\right)^2=2\left(2m-2\right)^2\)

=>\(\Leftrightarrow\left(\dfrac{m-3}{2m-2}\right)^2=\dfrac{2}{\sqrt{11}}\)

=>\(\left[{}\begin{matrix}\dfrac{m-3}{2m-2}=\sqrt{\dfrac{2}{\sqrt{11}}}\\\dfrac{m-3}{2m-2}=-\sqrt{\dfrac{2}{\sqrt{11}}}\end{matrix}\right.\)

mà m nguyên

nên \(m\in\varnothing\)

\(1.x^2+\dfrac{1}{x^2}-2m\left(x+\dfrac{1}{x}\right)+1+2m=0\left(1\right)\)\(đặt:x^2+\dfrac{1}{x^2}=t\)

\(x>0\Rightarrow t\ge2\sqrt{x^2.\dfrac{1}{x^2}}=2\)

\(x< 0\Rightarrow-t=-x^2+\dfrac{1}{\left(-x^2\right)}\ge2\Rightarrow t\le-2\)

\(\Rightarrow t\in(-\infty;-2]\cup[2;+\infty)\left(2\right)\)

\(\Rightarrow\left(1\right)\Leftrightarrow t^2-2mt+2m-1=0\)

\(\Leftrightarrow\left(t-1\right)\left(t-2m+1\right)=0\Leftrightarrow\left[{}\begin{matrix}t=1\notin\left(2\right)\\t=2m-1\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}2m-1\le-2\\2m-1\ge2\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}m\le-\dfrac{1}{2}\\m\ge\dfrac{3}{4}\end{matrix}\right.\)

\(2.\)  \(f^2\left(\left|x\right|\right)+\left(m-2\right)f\left(\left|x\right|\right)+m-3=0\left(1\right)\)

\(\Leftrightarrow\left[{}\begin{matrix}f\left(\left|x\right|\right)=-1\\f\left(\left|x\right|\right)=3-m\end{matrix}\right.\)

\(dựa\) \(vào\) \(đồ\) \(thị\) \(f\left(\left|x\right|\right)\) \(\Rightarrow f\left(\left|x\right|\right)=-1\) \(có\) \(2nghiem\) \(pb\)

\(\left(1\right)có\) \(6\) \(ngo\) \(pb\Leftrightarrow\left\{{}\begin{matrix}-1< 3-m< 3\\3-m\ne-1\\\end{matrix}\right.\)\(\Leftrightarrow0< m< 4\)

\(\Rightarrow m=\left\{1;2;3\right\}\)

1, y' = \(\dfrac{m^2-9}{\left(3x-m\right)^2}\)

ycbt <=> \(\left\{{}\begin{matrix}m^2-9< 0\\\dfrac{m}{-3}\ne x\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-3< m< 3\\m\ge0\end{matrix}\right.\)

\(\Leftrightarrow0\le m\le3\)

\(\sqrt{1+\dfrac{1}{x^2}+\dfrac{1}{\left(x+1\right)^2}}=\sqrt{\dfrac{x^2+\left(x+1\right)^2+x^2\left(x+1\right)^2}{x^2\left(x+1\right)^2}}=\sqrt{\dfrac{x^2\left(x+1\right)^2+2x^2+2x+1}{x^2\left(x+1\right)^2}}\)

\(=\sqrt{\dfrac{\left(x^2+x\right)^2+2\left(x^2+x\right)+1}{\left(x^2+x\right)^2}}=\sqrt{\dfrac{\left(x^2+x+1\right)^2}{\left(x^2+x\right)^2}}=\dfrac{x^2+x+1}{x^2+x}\)

\(=1+\dfrac{1}{x}-\dfrac{1}{x+1}\)

\(\Rightarrow f\left(1\right).f\left(2\right)...f\left(2020\right)=5^{1+1-\dfrac{1}{2}+1+\dfrac{1}{2}-\dfrac{1}{3}+...+1+\dfrac{1}{2020}-\dfrac{1}{2021}}\)

\(=5^{2021-\dfrac{1}{2021}}\)

\(\Rightarrow\dfrac{m}{n}=2021-\dfrac{1}{2021}=\dfrac{2021^2-1}{2021}\)

\(\Rightarrow m-n^2=2021^2-1-2021^2=-1\)