Bài 2: 

a: Xét tứ giác ABOC có

\(\widehat{ABO}+\widehat{ACO}=180^0\)

Do đó: ABOC là tứ giác nội tiếp

a: =3(x-y)(x+y)

\(a,=3\left(x-y\right)\left(x+y\right)\\ b,=2x\left(x^2-25\right)=2x\left(x-5\right)\left(x+5\right)\\ c,=5x\left(x^2-2x+1\right)=5x\left(x-1\right)^2\\ d,=\left(x-y\right)\left(x+y\right)+2\left(x-y\right)=\left(x-y\right)\left(x+y+2\right)\\ e,=x\left(y-3\right)+y\left(y-3\right)=\left(y-3\right)\left(x+y\right)\\ f,=\left(x+2\right)^2-16y^2=\left(x-4y+2\right)\left(x+4y+2\right)\)

12) \(4C_xH_y\left(COOH\right)_2+\left(2x+y+2\right)O_2\xrightarrow[]{t^o}\left(4x+8\right)CO_2+\left(2y+4\right)H_2O\)

13) \(2KHCO_3+Ca\left(OH\right)_2\rightarrow K_2CO_3+CaCO_3+2H_2O\)

14) \(Al_2O_3+6KHSO_4\rightarrow Al_2\left(SO_4\right)_3+3K_2SO_4+3H_2O\)

15) \(xFe_2O_3+\left(3x-2y\right)H_2\xrightarrow[]{t^o}2Fe_xO_y+\left(3x-2y\right)H_2O\)

\(2,\Leftrightarrow\left\{{}\begin{matrix}20x+25y-10xy=0\\20x-30y+xy=0\end{matrix}\right.\Leftrightarrow55y-11xy=0\\ \Leftrightarrow11y\left(5-x\right)=0\Leftrightarrow\left[{}\begin{matrix}y=0\\x=5\end{matrix}\right.\)

Với \(y=0\Leftrightarrow4x+0=0\Leftrightarrow x=0\)

Với \(x=5\Leftrightarrow20+5y=10y\Leftrightarrow y=4\)

Vậy \(\left(x;y\right)=\left\{\left(0;0\right);\left(5;4\right)\right\}\)

a) \(\sqrt{x-8}\) xác định khi

\(x-8\ge0\Leftrightarrow x\ge8\)

b) \(\sqrt{3x+1}\) xác định khi

\(3x+1\ge0\Leftrightarrow3x\ge-1\Leftrightarrow x\le-\dfrac{1}{3}\)

c) \(\sqrt{x^2+1}\) 

Ta có: \(x^2\ge0\Rightarrow x^2+1\ge0\)

Vậy biểu thức được xác định với mọi x

d) \(\sqrt{\left(x-6\right)\left(x+3\right)}\)

Xác định khi

\(\left\{{}\begin{matrix}\left\{{}\begin{matrix}x-6\ge0\\x+3\ge0\end{matrix}\right.\\\left\{{}\begin{matrix}x-6< 0\\x+3\ge0\end{matrix}\right.\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}\left\{{}\begin{matrix}x\ge6\\x\ge-3\end{matrix}\right.\\\left\{{}\begin{matrix}x< 6\\x< -3\end{matrix}\right.\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x\ge6\\x< -3\end{matrix}\right.\)

e) \(\sqrt{\dfrac{-2}{x-5}}\) xác định khi

\(\left\{{}\begin{matrix}\dfrac{-2}{x-5}\ge0\\x-5\ne0\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x\le5\\x\ne5\end{matrix}\right.\)

\(\Leftrightarrow x< 5\)

f) \(\dfrac{4}{\sqrt{x+3}}\) xác định khi

\(x+3>0\)

\(\Leftrightarrow x>-3\)

g) \(\dfrac{6x-2}{\sqrt{x}-3}\)

Xác định khi:

\(\left\{{}\begin{matrix}\sqrt{x}\ge0\\\sqrt{x}-3\ne0\end{matrix}\right.\)

\(\left\{{}\begin{matrix}x\ge0\\x\ne9\end{matrix}\right.\)

h) \(\sqrt{x^2-16}=\sqrt{\left(x+4\right)\left(x-4\right)}\)

Xác định khi
\(\left\{{}\begin{matrix}\left\{{}\begin{matrix}x+4< 0\\x-4< 0\end{matrix}\right.\\\left\{{}\begin{matrix}x+4\ge0\\x-4\ge0\end{matrix}\right.\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}\left\{{}\begin{matrix}x< -4\\x< 4\end{matrix}\right.\\\left\{{}\begin{matrix}x\ge-4\\x\ge4\end{matrix}\right.\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x< -4\\x\ge4\end{matrix}\right.\)

what is her mother going to prepare for her bỉthdat party

there are three sticks of butter in the cupboard

i have enough food for the first three day of your stay

không cần làm bài 1 với cả câu d bài 4 đâu nhé các bạn

cảm ơn mọi người

6B

10C

8A