Cảm ơn đã nhắc ạ 

BT8:

\(m_{Fe}=\dfrac{28\%.400}{100\%}=112g\)

\(\Rightarrow n_{Fe}=\dfrac{112}{56}=2mol\)

\(m_S=\dfrac{24\%.400}{100\%}=96g\)

\(\Rightarrow n_S=\dfrac{90}{32}=3mol\)

\(m_O=\dfrac{48\%.400}{100\%}=192g\)

\(\Rightarrow n_O=\dfrac{192}{16}=12mol\)

Vậy CTHH của Y: \(Fe_2SO_{12}\)

program tinh;

uses crt;

var a, b : integer;

begin

clrscr;

write('nhap so nguyen a :');redaln(a);

write('nhap so nguyen b:');readln(b);

writeln('gia tri cua bieu thuc 1 la :', (a + b)*(a - b));

writeln('gia tri cua bieu thuc 2 la :', a*a*a - b*b*b);

writeln('gia tri cua bieu thuc 3 la :', a*a*a - 2*a*b + b*b);

writeln('gia tri cua bieu thuc 4 la :', (a - b)/(a + b));

readln

end.

BT7:

\(PTK_{Q\text{ξ }tnhom}=1,275.\left(16+64\right)=102đvc\)

Mà: \(m_{Al}=\dfrac{4,5}{4}.m_{O_2}\)

Có: \(m_{Al}+m_{O_2}=102đvc\)

\(\Leftrightarrow\dfrac{4,5}{3}.m_{O_2}+m_{O_2}=102đvc\)

\(\Leftrightarrow M_{O_2}\left(\dfrac{4,5}{4}+1\right)=102đvc\)

\(\Leftrightarrow m_{O_2}=\dfrac{102}{\dfrac{4,5}{4}+1}\)

\(\Leftrightarrow m_{O_2}=48\left(1\right)\)

\(\rightarrow m_{Al}=102-48=54\left(2\right)\)

\(\left(1\right)\Rightarrow1molOxi:n_{O_2}=\dfrac{48}{16}=3mol\)

\(\left(2\right)\Rightarrow1mol\) nhôm: \(n_{Al}=\dfrac{54}{27}=2\)

Vậy CTHH là \(Al_2O_3\)

Integer: nguyên

String: xâu kí tự

Char: kí tự

Real: thực

Chọn Real

4. I wish it had not been cold last night.

5. I wish they worked fastly.

6. I wish she joined in the trip.

7. I wish i were good at English.

8. I wish he studied well. 

Áp dụng hệ thức cạnh và góc vào \(\text{Δ}ABC\) vuông tại A có \(AH\perp BC\) được:

\(AH^2=BH.CH\Leftrightarrow AH=\sqrt{BH.CH}=\sqrt{4.9}=6\)

Hay \(x=6\)

\(AC^2=BC.CH\Leftrightarrow AC=\sqrt{\left(BH+CH\right).CH}=\sqrt{\left(4+9\right).3\sqrt{13}}\)

Hay \(x=6;y=3\sqrt{13}\)

Câu 32: worried

Câu 33: copied

Câu 34: cried

Câu 35: discovered

EX 1: If i have a lot of money, i will buy a new house.

EX 2: If he has a lot of money, he will buy a new house.

EX 3: If she were at the party, she would meet Cam Ly singer.

1. I wish i knew many English words.

2. I wish my friend could stay with me longer.

3. I wish i had time to go around the city. 

4. I wish we had a computer therefore we could get access to the Internet. 

5. I wish i could go to the car show at the city show ground.