Bài 3:

\(n_{HCl}=3,5.0,2=0,7\left(mol\right)\)

Gọi x,y lần lượt là số mol của CuO, Fe₂O₃

Pt: \(CuO+2HCl\rightarrow CuCl_2+H_2O\) (1)

x \(\rightarrow\) 2x

\(Fe_2O_3+6HCl\rightarrow2FeCl_3+3H_2O\) (2)

y \(\rightarrow\) 6y

Theo gt: m_hh = 80x + 160y = 20 (3)

(1)(2)(3) \(\Rightarrow\left\{{}\begin{matrix}2x+6y=0,7\\80x+160y=20\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}x=0,05\\y=0,1\end{matrix}\right.\)

\(m_{CuO}=0,05.80=4\left(g\right)\)

\(m_{Fe_2O_3}=0,1.160=16\left(g\right)\)

Bài 4:

\(n_{CO_2}=\dfrac{2,24}{22,4}=0,1\left(mol\right)\)

Pt: \(Ba\left(OH\right)_2+CO_2\rightarrow BaCO_3+H_2O\)

0,1 mol \(\leftarrow0,1mol\) \(\rightarrow0,1mol\)

\(\Rightarrow C_{M_{Ba\left(OH\right)_2}}=\dfrac{0,1}{0,2}=0,5M\)

\(m_{BaCO_3}=0,1.197=19,7\left(g\right)\)

\(9x^2-72x=0\)

\(\Leftrightarrow9x\left(x-8\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}9x=0\\x-8=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=8\end{matrix}\right.\)

Vậy..

a) \(x^3-5x^2+x-5=0\)

\(\Leftrightarrow\left(x-5\right)\left(x^2+1\right)=0\)

Vì \(x^2+1>0\)

\(\Rightarrow x-5=0\)

\(\Rightarrow x=5\)

Vậy...

b) Mình nghĩ là sai đề nên sửa lại nhé :

\(x^4-2x^3+10x^2-20x=0\)

\(\Leftrightarrow\) \(x^3\left(x-2\right)+10x\left(x-2\right)=0\)

\(\Leftrightarrow\left(x-2\right)\left(x^3+10x\right)=0\)

\(\Leftrightarrow\left(x-2\right)x\left(x^2+10\right)=0\)

Vì \(x^2+10>0\)

\(\Rightarrow\left\{{}\begin{matrix}x=0\\x-2=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=0\\x=2\end{matrix}\right.\)

Vậy...

1. The present and past tense:

Act: S + V + Object

P: S + tobe + P.P ( V₃ ) (+ by) + O

2. Modal verbs

Act: S + M + V_(inf) + O

P: S + M + be + V₃ (+ by) + O

3. Present and past continuos tense:

Act: S + tobe + V_-ing + O

P: S + tobe + being + V₃ (+ by) + O

4. The present and past perfect tense:

Act: S + \(\left\{{}\begin{matrix}have\\has\\had\end{matrix}\right.\) + P.P + O

P: S + \(\left\{{}\begin{matrix}have\\has\\had\end{matrix}\right.\) + been + P.P (+ by) + O

Cô ơi ..