8:

a: Xét ΔAFB và ΔCFI có

góc FAB=góc FCI

góc AFB=góc CFI

=>ΔAFB đồng dạng với ΔCFI

b: Xét ΔEAB và ΔEKD có

góc EAB=góc EKD

góc AEB=góc KED

=>ΔEAB đồng dạng với ΔEKD

=>AB/KD=EA/EK

=>AB*EK=EA*KD

a) \(n_{MgCO_3}=\dfrac{33,6}{84}=0,4\left(mol\right)\)

PTHH: MgCO₃ + 2HNO₃ --> Mg(NO₃)₂ + CO₂ + H₂O

_______0,4---->0,8----------->0,4

\(C_{M\left(HNO_3\right)\left(C\right)}=\dfrac{0,8}{0,5}=1,6M\)

\(C_{M\left(Mg\left(NO_3\right)_2\right)\left(D\right)}=\dfrac{0,4}{0,5}=0,8M\)

b) Gọi \(\left\{{}\begin{matrix}C_{M\left(A\right)}=aM\\C_{M\left(B\right)}=bM\end{matrix}\right.\)

300ml dd A chứa: 0,3a mol HNO₃

200ml dd B chứa: 0,2b mol HNO₃

=> 0,3a + 0,2b = 0,8 (1)

200ml dd A chứa: 0,2a mol HNO₃

300ml dd B chứa: 0,3b mol HNO₃

=> \(\dfrac{0,2a+0,3b}{0,5}=1,4\) (2)

(1)(2) => a = 2 ; b = 1

1)\(\dfrac{5}{6}\)

2)\(\dfrac{1}{4}\)

3)\(\dfrac{12}{5}\)

4)\(\dfrac{39}{2}\)

5)\(1\)

Bài 8:

a: \(x^3+9x^2+27x+27=\left(x+3\right)^3\)

c: \(8-12x+6x^2-x^3=\left(2-x\right)^3\)

\(A=-2a^4bc^3\)-> bậc 8 

bài1

1. john began playing chess half an hour ago

=>john's.......been playing chess since a hour...........

2.they won't be able to come on sunday

=>it will...........be impossible for them to come on sunday........

3. we arrived too late to see the first film

=>we did.........not arrive early enough to see the first film............

4. this is his first visit to england

=>he's...........visiting England for the first time.............

bài 2

1. we/ not think/ play/ write/ Shakespeare

=> we don't think Shakespeare play and write

2. You/ tell/ how/ do it/ as soon/ you/get there

=> you will tell how to do as soon as you get there

3. Mai/find/hard/concentrate/her book/because/ noise

=> Mai finds it hard to concentrate on her book because of the noise

Có một vài câu bạn trước làm chưa đúng nên mình xin sửa lại

bài1

1. john began playing chess half an hour ago

=>john's played chess for half an hour

4. this is his first visit to england

=>he's never visited England before

bài 2

1. we/ not think/ play/ write/ Shakespeare

We don't think the play was written by Shakespeare

2. You/ tell/ how/ do it/ as soon/ you/get there

You will be told how to do it as soon as you get there

a) bên đường: trạng ngữ

cây cối : cái gì

xanh um: thế nào

a nhe

B.nhà cửa thưa thớt dần