Bài 3:

\(b,\Leftrightarrow\left(x+8\right)\left(x+8-3x\right)=0\\ \Leftrightarrow\left(x+8\right)\left(8-2x\right)=0\\ \Leftrightarrow2\left(4-x\right)\left(x+8\right)=0\Leftrightarrow\left[{}\begin{matrix}x=4\\x=-8\end{matrix}\right.\)

a)

nSO2=3,36 / 22,4=0,15 mol

Cu +2H2SO4 đ -t°-> CuSO4+SO2+2H2O

=> nCu = nSO2 = CuSO4 = 0,15 mol

mCuSO4=0,15.160=24g

mZnSO4=56,2-24=32,2g

nZnSO4=nZnO= 32,2/161=0,2 mol

m=mCu+mZnO=0,15.64+0,2.81=25,8g

b)

nH2SO4 pư=2nCu+nZnO=2.0,15+0,2=0,5 mol

nH2SO4 dư=0,5.10%=0,05mol

H2SO4+BaCl2 -> BaSO4+2HCl

nH2SO4dư=nBaSO4=0,05mol

mBaSO4=0,05.233=11,65g

chụp lại ảnh đi bn, khó nhìn quá, để xa máy ảnh ra  và đừng cắt ảnh

a) 

P1:

\(n_{Br_2}=\dfrac{80.20\%}{160}=0,1\left(mol\right)\)

PTHH: C₂H₄ + Br₂ --> C₂H₄Br₂

             0,1<--0,1

=> \(n_{C_2H_4\left(P_1\right)}=0,1\left(mol\right)\)

=> \(m_{C_3H_8\left(P_1\right)}=\dfrac{12,2}{2}-0,1.28=3,3\left(g\right)\)

=> \(n_{C_3H_8\left(P_1\right)}=\dfrac{3,3}{44}=0,075\left(mol\right)\)

=> \(V=\left(0,1.2+0,075,2\right).22,4=7,84\left(l\right)\)

\(\left\{{}\begin{matrix}\%V_{C_2H_4}=\dfrac{0,1}{0,1+0,075}.100\%=57,143\%\\\%V_{C_3H_8}=\dfrac{0,075}{0,1+0,075}.100\%=42,857\%\end{matrix}\right.\)

b) P₂ \(\left\{{}\begin{matrix}C_2H_4:0,1\left(mol\right)\\C_3H_8:0,075\left(mol\right)\end{matrix}\right.\)

Bảo toàn C: \(n_{CO_2}=0,425\left(mol\right)\) => \(n_{BaCO_3}=0,425\left(mol\right)\)

Bảo toàn H: \(n_{H_2O}=0,5\left(mol\right)\)

Xét \(\Delta m=m_{CO_2}+m_{H_2O}-m_{BaCO_3}=0,425.44+0,5.18-0,425.197=-56,025\left(g\right)\)

=> khối lượng dd sau pư giảm 56,025 gam

Bài 3: 

b: Ta có: \(\sqrt{x^2-2x+1}=\left|x-2\right|\)

\(\Leftrightarrow\left|x-1\right|=\left|x-2\right|\)

\(\Leftrightarrow x-1=2-x\)

\(\Leftrightarrow2x=3\)

hay \(x=\dfrac{3}{2}\)

Bài 4: ĐK: x>0

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

\(\Leftrightarrow B=\dfrac{\sqrt{x}\left[\left(\sqrt{x}\right)^3+1\right]}{x-\sqrt{x}+1}+1-\dfrac{\sqrt{x}\left(2\sqrt{x}+1\right)}{\sqrt{x}}\)

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

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

\(\Leftrightarrow B=x-\sqrt{x}\)

Vậy với x>0 thì \(B=x-\sqrt{x}\)

b) Ta có: \(B=2\)

\(\Leftrightarrow x-\sqrt{x}=2\)

\(\Leftrightarrow x-\sqrt{x}-2=0\)

 \(\Leftrightarrow x-2\sqrt{x}+\sqrt{x}-2=0\)

\(\Leftrightarrow\sqrt{x}.\left(\sqrt{x}-2\right)+\left(\sqrt{x}-2\right)=0\) 

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

Do \(\sqrt{x}+1>0\) nên, ta suy ra:

\(\sqrt{x}-2=0\Leftrightarrow\sqrt{x}=2\Leftrightarrow x=4\) \(\left(TMĐK\right)\)

Vậy \(x=4\) thì \(B=2\)

Bài 4: 

a: Ta có: \(B=\dfrac{x^2+\sqrt{x}}{x-\sqrt{x}+1}-\dfrac{2x+\sqrt{x}}{\sqrt{x}}+1\)

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

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

\(=x-\sqrt{x}\)

b: Để B=2 thì \(x-\sqrt{x}-2=0\)

\(\Leftrightarrow\sqrt{x}-2=0\)

hay x=4

b.

\(\Leftrightarrow\dfrac{\sqrt{3}}{2}cos2x-\dfrac{1}{2}sin2x=-cosx\)

\(\Leftrightarrow cos\left(2x+\dfrac{\pi}{6}\right)=cos\left(x+\pi\right)\)

\(\Leftrightarrow\left[{}\begin{matrix}2x+\dfrac{\pi}{6}=x+\pi+k2\pi\\2x+\dfrac{\pi}{6}=-x-\pi+k2\pi\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{5\pi}{6}+k2\pi\\x=-\dfrac{7\pi}{18}+\dfrac{k2\pi}{3}\end{matrix}\right.\)

c.

\(\Leftrightarrow2cos4x.sin3x=2sin4x.cos4x\)

\(\Leftrightarrow cos4x\left(sin4x-sin3x\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}cos4x=0\\sin4x=sin3x\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}4x=\dfrac{\pi}{2}+k\pi\\4x=3x+k2\pi\\4x=\pi-3x+k2\pi\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{\pi}{8}+\dfrac{k\pi}{4}\\x=k2\pi\\x=\dfrac{\pi}{7}+\dfrac{k2\pi}{7}\end{matrix}\right.\)

2.

\(f\left(x\right)=\dfrac{1}{2}-\dfrac{1}{2}cos2x-\dfrac{\sqrt{3}}{2}sin2x-5\)

\(=-\dfrac{9}{2}-\left(\dfrac{1}{2}cos2x+\dfrac{\sqrt{3}}{2}sin2x\right)\)

\(=-\dfrac{9}{2}-cos\left(2x-\dfrac{\pi}{3}\right)\)

Do \(-1\le-cos\left(2x-\dfrac{\pi}{3}\right)\le1\Rightarrow-\dfrac{11}{2}\le y\le-\dfrac{7}{2}\)

\(y_{min}=-\dfrac{11}{2}\) khi \(cos\left(2x-\dfrac{\pi}{3}\right)=1\Leftrightarrow x=\dfrac{\pi}{6}+k\pi\)

\(y_{max}=-\dfrac{7}{2}\) khi \(cos\left(2x-\dfrac{\pi}{3}\right)=-1\Rightarrow x=\dfrac{2\pi}{3}+k\pi\)

Help

B

C

B

Câu 18 : A

Câu 19 : A

Câu 20 : B

A

A

D