Dear My friend

I live in Ha Noi. It’s the capital of Vietnam. I’ve been living here for 5 years and I believe it’s the place that suits me most. The city has great culture to explore and offers good opportunities of career and education.People who live here is very friendly and helpful. But the crowded congested traffic is a real issue here, it’s an ideal place to meet people from over the world. It’s always changing so you’ll hardly get bored at this sleepless city.

Best regards,

(Your name)

a: Thay x=-4 vào B, ta được:

\(B=\dfrac{1-2\cdot\left(-4\right)}{2-\left(-4\right)}=\dfrac{1+8}{2+4}=\dfrac{9}{6}=\dfrac{3}{2}\)

Bài 2: 

a: =>168x+20=6x-21

=>162x=-41

hay x=-41/162

b: \(\Leftrightarrow2\left(3x-8\right)=3\left(5-x\right)\)

=>6x-16=15-3x

=>9x=31

hay x=31/9

c: \(\Leftrightarrow4\left(x^2+8x-20\right)-\left(x+4\right)\left(x+10\right)=3\left(x^2+2x-8\right)\)

\(\Leftrightarrow4x^2+32x-80-x^2-14x-40-3x^2-6x+24=0\)

=>12x-96=0

hay x=8

mình làm những bài bn chưa lm nhé

9B

10A

bài 2

have repainted

bàii 3

ride - walikking

swimming

watch

2 have repainted

4 have done 

8 have stepped

9 have you ever played

7) 1 riding -walking

2 swimming

3 watching

8)

2 my mother doesn't like listening to music

5 doing more exercises makes you healthier

còn lại ok nha

chịu ???????????????????

1) Áp dụng định lí Pytago vào ΔABC vuông tại A, ta được:

\(BC^2=AB^2+AC^2\)

\(\Leftrightarrow BC^2=6^2+8^2=100\)

hay BC=10(cm)

Áp dụng hệ thức lượng trong tam giác vuông vào ΔABC vuông tại A có AH là đường cao ứng với cạnh huyền BC, ta được:

\(AH\cdot BC=AB\cdot AC\)

\(\Leftrightarrow AH\cdot10=6\cdot8=48\)

hay AH=4,8(cm)

\(A=\dfrac{3}{2}-tana\cdot cos^2a\)

\(=\dfrac{3}{2}-\dfrac{sina}{cosa}\cdot cos^2a\)

\(=\dfrac{3}{2}-sina\cdot cosa\)

\(=\dfrac{3}{2}-\dfrac{1}{2}sin2a\)
\(0^0< a< 90^0\)

=>\(0< =2a< =180^0\)

=>\(sin2a\in\left[-1;1\right]\)

\(-1< =sin2a< =1\)

=>\(\dfrac{1}{2}>=-\dfrac{1}{2}sin2a>=-\dfrac{1}{2}\)

=>\(\dfrac{7}{2}>=-\dfrac{1}{2}sin2a+3>=\dfrac{5}{2}\)

=>\(\dfrac{5}{2}< =y< =\dfrac{7}{2}\)

\(y_{min}=\dfrac{5}{2}\) khi sin2a=1

=>\(2a=\dfrac{\Omega}{2}+k2\Omega\)

=>\(a=\dfrac{\Omega}{4}+k\Omega\)

mà 0<a<90

nên a=45