a: Xét (O) có

\(\widehat{BAC}\) là góc nội tiếp chắn cung BC

Do đó: \(sđ\stackrel\frown{BC}=\widehat{BOC}=2\cdot\widehat{BAC}=120^0\)

b: M là điểm chính giữa của cung BC

=>\(sđ\stackrel\frown{MB}=sđ\stackrel\frown{MC}=\dfrac{sđ\stackrel\frown{BC}}{2}=60^0\)

Xét (O) có \(\widehat{AIB}\) là góc có đỉnh ở bên trong đường tròn chắn hai cung AB và MC

nên \(\widehat{AIB}=\dfrac{1}{2}\cdot\left(sđ\stackrel\frown{AB}+sđ\stackrel\frown{MC}\right)\)

=>\(\widehat{AIB}=\dfrac{1}{2}\left(sđ\stackrel\frown{AB}+sđ\stackrel\frown{MB}\right)=\dfrac{1}{2}\left(100^0+60^0\right)=80^0\)

Xét (O) có

\(\widehat{AMC}\) là góc nội tiếp chắn cung AC

\(\widehat{ABC}\) là góc nội tiếp chắn cung AC

Do đó: \(\widehat{AMC}=\widehat{ABC}=70^0\)

=>\(\widehat{AIB}>\widehat{AMC}\)

a) \(P=\dfrac{x}{\left(\sqrt{x}+\sqrt{y}\right)\left(1-\sqrt{y}\right)}-\dfrac{y}{\left(\sqrt{x}+\sqrt{y}\right)\left(1+\sqrt{x}\right)}-\dfrac{xy}{\left(\sqrt{x}+1\right)\left(1-\sqrt{y}\right)}\)

ĐK: \(\left\{{}\begin{matrix}x\ge0;y\ge0\\\sqrt{x}+\sqrt{y}\ne0\\\sqrt{x}+1\ne0\\1-\sqrt{y}\ne0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x\ge0;y\ge0\\x^2+y^2>0\\y\ne1\end{matrix}\right.\) 

\(P=\dfrac{x\left(\sqrt{x}+1\right)}{\left(\sqrt{x}+\sqrt{y}\right)\left(1-\sqrt{y}\right)\left(\sqrt{x}+1\right)}-\dfrac{y\left(1-\sqrt{y}\right)}{\left(\sqrt{x}+\sqrt{y}\right)\left(1-\sqrt{y}\right)\left(\sqrt{x}+1\right)}-\dfrac{xy\left(\sqrt{x}+\sqrt{y}\right)}{\left(\sqrt{x}+\sqrt{y}\right)\left(1-\sqrt{y}\right)\left(\sqrt{x}+1\right)}\)

\(P=\dfrac{x\sqrt{x}+x-y+y\sqrt{y}-xy\sqrt{x}-xy\sqrt{y}}{\left(\sqrt{x}+\sqrt{y}\right)\left(1-\sqrt{y}\right)\left(\sqrt{x}+1\right)}\)

\(P=\dfrac{\left(x\sqrt{x}+y\sqrt{y}\right)+\left(x-y\right)-\left(xy\sqrt{x}+xy\sqrt{y}\right)}{\left(\sqrt{x}+\sqrt{y}\right)\left(1-\sqrt{y}\right)\left(\sqrt{x}+1\right)}\)

\(P=\dfrac{\left(\sqrt{x}+\sqrt{y}\right)\left(x-\sqrt{xy}+y\right)+\left(\sqrt{x}+\sqrt{y}\right)\left(\sqrt{x}-\sqrt{y}\right)-xy\left(\sqrt{x}+\sqrt{y}\right)}{\left(\sqrt{x}+\sqrt{y}\right)\left(1-\sqrt{y}\right)\left(\sqrt{x}+1\right)}\)

\(P=\dfrac{\left(\sqrt{x}+\sqrt{y}\right)\left(x-\sqrt{xy}+y+\sqrt{x}-\sqrt{y}-xy\right)}{\left(\sqrt{x}+\sqrt{y}\right)\left(1-\sqrt{y}\right)\left(\sqrt{x}+1\right)}\)

\(P=\dfrac{\left(x-xy\right)+\left(-\sqrt{y}+y\right)+\left(\sqrt{x}-\sqrt{xy}\right)}{\left(1-\sqrt{y}\right)\left(\sqrt{x}+1\right)}\)

\(P=\dfrac{x\left(1-y\right)-\sqrt{y}\left(1-\sqrt{y}\right)+\sqrt{x}\left(1-\sqrt{y}\right)}{\left(1-\sqrt{y}\right)\left(\sqrt{x}+1\right)}\)

\(P=\dfrac{x\left(1-\sqrt{y}\right)\left(1+\sqrt{y}\right)-\sqrt{y}\left(1-\sqrt{y}\right)+\sqrt{x}\left(1-\sqrt{y}\right)}{\left(1-\sqrt{y}\right)\left(\sqrt{x}+1\right)}\)

\(P=\dfrac{\left(1-\sqrt{y}\right)\left(x+x\sqrt{y}-\sqrt{y}+\sqrt{x}\right)}{\left(1-\sqrt{y}\right)\left(\sqrt{x}+1\right)}\)

\(P=\dfrac{x+x\sqrt{y}-\sqrt{y}+\sqrt{x}}{\sqrt{x}+1}\)   

\(P=\dfrac{\left(x+\sqrt{x}\right)+\left(x\sqrt{y}-\sqrt{y}\right)}{\sqrt{x}+1}\)

\(P=\dfrac{\sqrt{x}\left(\sqrt{x}+1\right)+\sqrt{y}\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}{\sqrt{x}+1}\)

\(P=\dfrac{\left(\sqrt{x}+1\right)\left(\sqrt{x}+\sqrt{xy}-\sqrt{y}\right)}{\sqrt{x}+1}\)

\(P=\sqrt{x}+\sqrt{xy}-\sqrt{y}\)

b) \(P=2\) khi: 

\(\sqrt{x}+\sqrt{xy}-\sqrt{y}=2\)

\(\Leftrightarrow\sqrt{x}\left(\sqrt{y}+1\right)-\sqrt{y}-1=2-1\)

\(\Leftrightarrow\sqrt{x}\left(\sqrt{y}+1\right)-\left(\sqrt{y}+1\right)=1\)

\(\Leftrightarrow\left(\sqrt{x}-1\right)\left(\sqrt{y}+1\right)=1\)

Mà: x,y là nguyên \(\Rightarrow\sqrt{x}-1,\sqrt{y}+1\inƯ\left(1\right)=\left\{1;-1\right\}\)

Mặt khác: \(\sqrt{y}+1\ge1\) nên ta có:

\(\sqrt{y}+1=1\Leftrightarrow y=0\) (tm)

\(\Rightarrow\sqrt{x}-1=1\Leftrightarrow\sqrt{x}=2\Leftrightarrow x=4\) (tm) 

Vậy: \(\left(x;y\right)=\left(4;0\right)\)

\(P=\left(a^2+\dfrac{1}{16}+\dfrac{1}{16}+\dfrac{1}{16}\right)+\left(b^2+\dfrac{1}{16}+\dfrac{1}{16}+\dfrac{1}{16}\right)-\dfrac{3}{8}\)

\(P\ge4\sqrt[4]{\dfrac{a^2}{16^3}}+4\sqrt[4]{\dfrac{b^2}{16^3}}-\dfrac{3}{8}=\dfrac{1}{2}\left(\sqrt{a}+\sqrt{b}\right)-\dfrac{3}{8}=\dfrac{1}{8}\)

\(P_{min}=\dfrac{1}{8}\) khi \(a=b=\dfrac{1}{4}\)

Do \(\left\{{}\begin{matrix}a;b\ge0\\\sqrt{a}+\sqrt{b}=1\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}0\le a\le1\\0\le b\le1\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}\sqrt{a}\ge a^2\\\sqrt{b}\ge b^2\end{matrix}\right.\)

\(\Rightarrow a^2+b^2\le\sqrt{a}+\sqrt{b}=1\)

\(P_{max}=1\) khi \(\left(a;b\right)=\left(1;0\right);\left(0;1\right)\)

Tuần trước tuần trở in

Do (d) đi qua A nên:

\(0.m+n=-1\Rightarrow n=-1\)

\(\Rightarrow y=mx-1\)

Pt hoành độ giao điểm (P) và (d):

\(\dfrac{1}{2}x^2=mx-1\Leftrightarrow x^2-2mx+2=0\) (1)

(d) tiếp xúc (P) khi và chỉ khi (1) có nghiệm kép

\(\Rightarrow\Delta'=m^2-2=0\Rightarrow m=\pm\sqrt{2}\)

- Với \(m=\sqrt{2}\Rightarrow x=-\dfrac{b}{2a}=\sqrt{2}\Rightarrow y=\dfrac{1}{2}x^2=1\)

Tọa độ tiếp điểm là \(\left(\sqrt{2};1\right)\)

- Với \(m=-\sqrt{2}\Rightarrow x=-\dfrac{b}{2a}=-\sqrt{2}\Rightarrow y=1\) 

Tọa độ tiếp điểm là \(\left(-\sqrt{2};1\right)\)

Ta có pt: \(x^2-2mx+m^2=0\)

\(\Delta=\left(-2m\right)^2-4\cdot1\cdot m^2=0\)

Khi phương trình luôn có nghiệm kép với mọi m \(\Rightarrow x_1< x_2\) vô lý 

Chỉ có thể tìm được m nếu \(2000< x_1=x_2< 2007\)  

Khi đó: \(x_1=x_2=\dfrac{-\left(-2m\right)}{2}=m\)

\(\Rightarrow2000< m< 2007\)

Các số nguyên m thỏa mãn là: 

\(m\in\left\{2001;2002;2003;2004;2005;2006\right\}\)

ĐKXĐ: \(x\ge-\dfrac{1}{2};x\ne0\)

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

\(\Leftrightarrow-\dfrac{x-1}{x^2}=\dfrac{x-1}{\sqrt{2x+1}+\sqrt{x+2}}\)

\(\Leftrightarrow\left(x-1\right)\left(\dfrac{1}{\sqrt{2x+1}+\sqrt{x+2}}+\dfrac{1}{x^2}\right)=0\)

\(\Leftrightarrow x-1=0\) (do \(\dfrac{1}{\sqrt{2x+1}+\sqrt{x+2}}+\dfrac{1}{x^2}\) luôn dương)

\(\Leftrightarrow x=1\)

Đk: \(x\ge-\dfrac{1}{2},x\ne0\)

pt \(\Leftrightarrow\dfrac{1}{x^2}-\dfrac{1}{x}=\sqrt{2x+1}-\sqrt{x+2}\)

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

\(\Leftrightarrow\dfrac{1-x}{x^2}=\dfrac{x-1}{\sqrt{2x+1}+\sqrt{x+2}}\)

\(\Leftrightarrow\left(x-1\right)\left(\dfrac{1}{\sqrt{2x+1}+\sqrt{x+2}}+\dfrac{1}{x^2}\right)=0\)

\(\Leftrightarrow x=1\) (vì \(\dfrac{1}{\sqrt{2x+1}+\sqrt{x+2}}+\dfrac{1}{x^2}>0\))

Vậy \(S=\left\{1\right\}\)