\(\text{PT }\left(d_1\right)\text{ giao }Ox:y=0\Leftrightarrow\dfrac{1}{2}x=-2\Leftrightarrow x=-4\Leftrightarrow A\left(-4;0\right)\Leftrightarrow OA=4\left(cm\right)\\ \text{PT }\left(d_2\right)\text{ giao }Ox:y=0\Leftrightarrow x=2\Leftrightarrow B\left(2;0\right)\Leftrightarrow OB=2\left(cm\right)\\ \Leftrightarrow AB=OA+OB=2+4=6\left(cm\right)\\ \text{PT hoành độ giao điểm: }\dfrac{1}{2}x+2=-x+2\Leftrightarrow x=0\Leftrightarrow y=2\Leftrightarrow C\left(0;2\right)\Leftrightarrow OC=2\left(cm\right)\\ \Leftrightarrow S_{ABC}=\dfrac{1}{2}OC\cdot AB=\dfrac{1}{2}\cdot2\cdot6=6\left(cm^2\right)\\ \left\{{}\begin{matrix}AC=\sqrt{2^2+4^2}=2\sqrt{5}\left(pytago\right)\left(cm\right)\\BC=\sqrt{2^2+2^2}=2\sqrt{2}\left(pytago\right)\left(cm\right)\end{matrix}\right.\\ \Leftrightarrow P_{ABC}=AB+BC+CA=2\sqrt{5}+2\sqrt{2}+6\left(cm\right)\)

ĐK: \(x,y\neq 0\)

\(PT\left(2\right)\Leftrightarrow x=9-y\)

Thay vào \(PT\left(1\right)\Leftrightarrow\dfrac{1}{9-y}+\dfrac{1}{y}=\dfrac{1}{2}\Leftrightarrow2y+18-2y=9y-y^2\)

\(\Leftrightarrow y^2-9y+18=0\\ \Leftrightarrow\left[{}\begin{matrix}y=3\Rightarrow x=6\\y=6\Rightarrow x=3\end{matrix}\right.\)

Vậy \(\left(x;y\right)=\left(6;3\right);\left(3;6\right)\)

Cho quỳ tím vào các mẫu thử:

- Quỳ hóa đỏ: \(NH_4Cl\)

- Quỳ hóa xanh: \(Na_2CO_3\)

- Quỳ ko đổi màu: \(NaNO_3\)

\(a,\Leftrightarrow x\left(x+5\right)=0\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-5\end{matrix}\right.\\ b,\Leftrightarrow3x\left(x-1\right)+\left(x-1\right)=0\\ \Leftrightarrow\left(x-1\right)\left(3x+1\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=1\\x=-\dfrac{1}{3}\end{matrix}\right.\\ c,\Leftrightarrow\left(x+2\right)\left(2x-3\right)=0\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=\dfrac{3}{2}\end{matrix}\right.\)

a, Đặt kim loại trung bình là R \(\rightarrow \) R hóa trị II

\(PTHH:R+2HCl\to RCl_2+H_2\\ \Rightarrow n_R=n_{H_2}=\dfrac{4,48}{22,4}=0,2(mol)\\ \Rightarrow M_R=\dfrac{6,5}{0,2}=32,5(g/mol)\)

Vậy 2 KL đó là Mg (24) và Ca (40)

\(b,\) Đặt \((n_{Mg};n_{Ca})=(x;y)(mol)\)

\(\Rightarrow \begin{cases} 24x+40y=6,5\\ x+y=n_{H_2}=0,2 \end{cases}\Rightarrow \begin{cases} x=0,09375(mol)\\ y=0,10625(mol) \end{cases}\\ \Rightarrow \begin{cases} m_{Mg}=2,25(g)\\ m_{Ca}=4,25(g) \end{cases}\)

\(n_{Fe}=\dfrac{5,6}{56}=0,1(mol)\\ a,PTHH:Fe+H_2SO_4\to FeSO_4+H_2\\ b,n_{H_2}=n_{Fe}=n_{H_2SO_4}=0,1(mol)\\ \Rightarrow V_{H_2}=0,1.22,4=2,24(l)\\ c,m_{dd_{H_2SO_4}}=\dfrac{0,1.98}{10\%}=98(g)\)

\(n_{H_2}=\dfrac{2,24}{22,4}=0,1(mol)\\ PTHH:Fe+2HCl\to FeCl_2+H_2\\ \Rightarrow n_{HCl}=2n_{H_2}=0,2(mol)\\ a,C_{M_{HCl}}=\dfrac{0,2}{0,1}=2M\\ b,n_{Fe}=n_{H_2}=0,1(mol)\\ \Rightarrow m_{Fe}=0,1.56=5,6(g)\\ \Rightarrow m_{Cu}=20-5,6=14,4(g)\\ c,\%m_{Fe}=\dfrac{5,6}{20}.100\%=28\%\\ \%m_{Cu}=100\%-28\%=72\%\)