a) xét tam giác AOB và tam giác COD, ta có :
OC = OA (gt)
góc DOC = góc BOA (đối đỉnh)
OD = OB (gt)
=> tam giác AOB = tam giác COD (c.g.c)
b) xét tam giác DON và tam giác BOM, ta có :
OD = OB (gt)
góc DON = góc BOM (đối đỉnh)
MN là cạnh chung
=> tam giác DON = tam giác BOM (c.g.c)
=> MB = ND (2 cạnh tương ứng)

em đồng tình về vấn đề với ý kiến trên

Question2: Rearrange the following words and phrased to make complete sentences.

most/ is/ house/ which/ for/ the/ and/ family/ suitable/ Mr.Nam/ his/ ?/
=> Which is the most suitable house for Mr.Nam and his family?

are/ in/ the/ playing/ the/ schoolyard/ corner/ marbles/ of/ boys/ a/ of/ some/.
=> Some of the boys are playing marbles in a corner of the schoolyard.

like/ walk/ a/ would/ have/ you/ show/ after/ musical/ the/ to/?/.
=> Would you to have a walk after the musical show ?

summer/ in/ students/ going/ the/ in/ school/ are/ my/ forty/ visit/ to/ citadel/ this/ Hue/ .
=> Forty students in my school are going to visit the citadel in Hue this summer

is/ one/ the/ after-school/ populer/ most/ USA/ of/ baseball/ the/ in/ activities
baseball is one of the most popular activities after school in the USSA

1. that is an intelligent dog

2. i took the bus to school

3. how many plums do you want to buy ?

4. i find collecting old comic bbooks interesting

câu a)

\(S=3^0+3^2+3^4+...+3^{2002}\\ \Rightarrow9S=3^2+3^4+3^6+...+3^{2004}\)

từ đó ta suy ra : \(9S-S=\left(3^2+3^4+...+3^{2004}\right)-\left(3^0+3^2+3^4+...+3^{2002}\right)\)

vậy \(8S=3^{2004}-1\Rightarrow S=\dfrac{3^{2004}-1}{8}\)

b) các số mũ lần lượt như sau : \(0;2;4;6;8;...;2002\)

ta có các dãy số hạng của những số trên là :

\(\left(2002-0\right)\div2+1=1002\) (số)

số nhóm mà chúng ta có thể ghép được là :

\(\dfrac{1002}{3}=334\) \(\left(nhóm\right)\)

\(\Rightarrow S=\left(3^0+3^2+3^4\right)+\left(3^6+3^8+3^{10}\right)+...+\left(3^{1998}+3^{2000}+3^{2002}\right)\\ \Rightarrow S=\left(3^0+3^2+3^4\right)+3^6\times\left(3^0+3^2+3^4\right)+...+3^{1998}\times\left(3^0+3^2+3^4\right)\\ \Rightarrow S=1\times91+3^6\times91+...+3^{1998}\times91=\left(1+3^6+...+3^{1998}\right)\times91\)TA CÓ 91 CHIA HẾT CHO 7 CHO NÊN TA KẾT LUẬN RẰNG S ⋮ 7

bài 1 : 

\(\dfrac{1}{6}=\dfrac{2}{12};\dfrac{12}{3}=\dfrac{48}{12};\dfrac{3}{36}=\dfrac{1}{12};10=\dfrac{120}{12}\)

BÀI NÀY MÌNH THẤY HƠI GIỐNG BÀI CỦA LỚP 7 NHA BẠN !

 bài 4 : lập các cặp phân số bằng nhau từ các tích sau : 

a) 3 x 8 = 4 x 6

\(\dfrac{3}{4}=\dfrac{6}{8};\dfrac{3}{6}=\dfrac{4}{8};\dfrac{4}{3}=\dfrac{8}{6};\dfrac{6}{3}=\dfrac{8}{4}\)

b) (-4) x 5 = (-2) x 10

\(\dfrac{-4}{10}=\dfrac{-2}{5};\dfrac{-4}{-2}=\dfrac{10}{5};\dfrac{10}{-4}=\dfrac{5}{-2};\dfrac{-2}{-4}=\dfrac{5}{10}\)

bài 5 : tìm \(x\)

1) \(180\div x=-12\)

\(x=180\div\left(-12\right)\\ x=-15\)

2) \(-15-x=-\left(-7\right)\)

\(-15-x=7\\ x=-15-7=-\left(15+7\right)\\ x=-22\)

3) \(-129-\left(35-x\right)=55\)

\(35-x=\left(-129\right)-55=-\left(129+55\right)\\ 35-x=-184\\ x=35-\left(-184\right)=35+184\\ x=219\)

4) \(2\times\left(x-6\right)^2-1=49\)

\(2\times\left(x-6\right)^2=50\\ \left(x-6\right)^2=50\div2=25\)

BÂY GIỜ CHÚNG GTA XÉT 2 TRƯỜNG HỢP

*trường hợp 1

\(\left(x-6\right)^2=5^2\\ \Rightarrow x-6=5\\ x=5+6\\ x=11\)

*trường hợp 2

\(\left(x-6\right)^2=\left(-5\right)^2\\ \Rightarrow x-6=-5\\ x=\left(-5\right)+6\\ x=1\)

5) \(\dfrac{x}{-15}=\dfrac{2}{3}\)

\(\Rightarrow x\times3=2\times\left(-15\right)\\ \Rightarrow x\times3=-30\\ \Rightarrow x=-10\)

6) \(\dfrac{-2}{5}=\dfrac{-12}{x}\)

\(\Rightarrow\left(-2\right)\times x=\left(-12\right)\times5\\ \Rightarrow\left(-2\right)\times=-60\\ \Rightarrow x=\left(-60\right)\div\left(-2\right)\\ \Rightarrow x=30\)

7) \(\dfrac{6}{5}=\dfrac{-12}{x}\)

\(\Rightarrow6\times x=\left(-12\right)\times5\Rightarrow6\times x=-60\\ \Rightarrow x=\left(-60\right)\div6\\ \Rightarrow x=-10\)

8) \(\dfrac{-9}{x}=\dfrac{3}{4}\)

\(\Rightarrow\left(-9\right)\times4=3\times x\\ \Rightarrow-36=3\times x\\ \Rightarrow x=\left(-36\right)\div3\\ x=-12\)

9) \(\dfrac{6}{5}=\dfrac{-24}{12-x}\)

\(\Rightarrow6\times\left(12-x\right)=\left(-24\right)\times5\\ \Rightarrow6\times\left(12-x\right)=-120\\ \Rightarrow12-x=\left(-120\right)\div6\\ \Rightarrow12-x=-20\\ \Rightarrow x=12-\left(-20\right)=12+20\\ x=32\)

10) \(\dfrac{2}{x+2}=\dfrac{1}{5}\)

\(\Rightarrow2\times5=1\times\left(x+2\right)\\ \Rightarrow10=1\times\left(x+2\right)\\ \Rightarrow x+2=10\\ \Rightarrow x=10-2\\ x=8\)

11) \(\dfrac{4}{x-1}=\dfrac{3}{15}\)

\(\Rightarrow4\times15=3\times\left(x-1\right)\\ \Rightarrow60=3\times\left(x-1\right)\\ \Rightarrow x-1=20\\ \Rightarrow x=21\)

- i was at home yesterday morning
- my name is subjects
- i'm very well
- i have maths, english
- i'm in class 1,2,3,4,5,6,7,8,9,10,11,12
- i played football

0,57 = 57%

0,3 = 30%

0,234 = 23,4%

1,35 = 135 %