kẻ CM//a và DN//bB(CM và Aa nằm cùng phía với nửa mặt phẳng chứa tia AC, DN và Bb nằm khác phía với nửa mặt phẳng chứa tia DB

CM//Aa

=>\(\widehat{MCA}=\widehat{A_1}\)

Ta có: CM//a

DN//b

mà a//b

nên CM//DN//a//b

CM//DN

=>\(\widehat{MCD}=\widehat{CDN}\)

DN//Bb

=>\(\widehat{NDB}=\widehat{B_1}\)

Ta có: \(\widehat{ACD}=\widehat{ACM}+\widehat{CDM}=\widehat{CDN}+\widehat{B_1}\)

\(\widehat{CDB}=\widehat{CDN}+\widehat{NDB}=\widehat{CDN}+\widehat{B_1}\)

Do đó: \(\widehat{ACD}=\widehat{CDB}\)

\(2n-1⋮2n+3\)

=>\(2n+3-4⋮2n+3\)

=>\(-4⋮2n+3\)

=>\(2n+3\in\left\{1;-1;2;-2;4;-4\right\}\)

=>\(2n\in\left\{-2;-4;-1;-5;1;-7\right\}\)

=>\(n\in\left\{-1;-2;-\dfrac{1}{2};-\dfrac{5}{2};\dfrac{1}{2};-\dfrac{7}{2}\right\}\)

\(2n+1⋮n+5\)

=>\(2n+10-9⋮n+5\)

=>\(-9⋮n+5\)

=>\(n+5\in\left\{1;-1;3;-3;9;-9\right\}\)

=>\(n\in\left\{-4;-6;-2;-8;4;-14\right\}\)

Ở thì hiện tại hoàn thành nhé mình cần gấp, cảm ơn các bạn 

1. She cooked the meal at this time yesterday.

cooked => was cooking 

2. His mother has just went to HCM city.

went => gone

3. What has she just say?

say => said

4. She's cuting grass in the garden now.

cuting => cutting

5. It's the first time he visits my family.

visits => has visited

6. When we came, they slept yesterday afternoon.

slept => were sleeping

7. Nam and his friend has found his keys.

has => have

8. I regret to inform that you fail the exam.

fail => have failed

9. She enjoyed collect stamp when she was young.

collect => collecting

10. We learn English for 3 years.

learn => have learned

11. She has been a nurse since she has graduated from the university.

has graduated => graduated

12. My mother is decorateing the room at the moment.

decorateing => decorating

13. She always is late for school.

always is => is always

14. My sister often doesn't go to the zoo on Monday.

often doesn't => doesn't often

15. His friends is tired today.

is = >are 

Bài 2:

Vì \(\widehat{xOz}< \widehat{xOy}\left(50^0< 80^0\right)\)

nên tia Oz nằm giữa hai tia Ox,Oy

=>\(\widehat{xOz}+\widehat{yOz}=\widehat{xOy}\)

=>\(\widehat{yOz}=80^0-50^0=30^0\)

Bài 4:

Ta có: \(\widehat{xEy}+\widehat{xEy'}=180^0\)(hai góc kề bù)

=>\(\widehat{xEy'}=180^0-50^0=130^0\)

Ta có: \(\widehat{xEy}=\widehat{x'Ey'}\)(hai góc đối đỉnh)

mà \(\widehat{xEy}=50^0\)

nên \(\widehat{x'Ey'}=50^0\)

Ta có: \(\widehat{xEy'}=\widehat{x'Ey}\)(hai góc đối đỉnh)

mà \(\widehat{xEy'}=130^0\)

nên \(\widehat{x'Ey}=130^0\)

Ta có:

\(-x^2+x-5\\ =-x^2+x-\dfrac{1}{4}+\dfrac{1}{4}-5\\ =-\left(x^2-x+\dfrac{1}{4}\right)+\dfrac{1}{4}-5\\ =-\left[x^2-2.\dfrac{1}{2}.x+\left(\dfrac{1}{2}\right)^2\right]-\dfrac{19}{4}\\ =-\left(x-\dfrac{1}{2}\right)^2-\dfrac{19}{4}\)

Nhận xét:

\(\left(x-\dfrac{1}{2}\right)^2\ge0,\forall x\\ \Rightarrow-\left(x-\dfrac{1}{2}\right)^2\le0,\forall x\\ \Rightarrow-\left(x-\dfrac{1}{2}\right)^2-\dfrac{19}{4}\le-\dfrac{19}{4},\forall x\)
hay \(-x^2+x-5\le-\dfrac{19}{4},\forall x\) 
Dấu "=" xảy ra khi và chỉ khi:
\(x-\dfrac{1}{2}\\=0\\ \Rightarrow x=\dfrac{1}{2}\)  
Vậy...

\(\left|x-2\right|>=0\forall x\)

\(\left|2x+y-z\right|>=0\forall x,y,z\)

\(\left|2z+1\right|>=0\forall z\)

Do đó: \(\left|x-2\right|+\left|2x+y-z\right|+\left|2z+1\right|>=0\forall x,y,z\)

mà \(\left|x-2\right|+\left|2x+y-z\right|+\left|2z+1\right|< =0\)

nên Dấu '=' xảy ra khi \(\left\{{}\begin{matrix}x-2=0\\2x+y-z=0\\2z+1=0\\\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}x=2\\z=-\dfrac{1}{2}\\y=-2x+z=-2\cdot2+\dfrac{-1}{2}=-4-\dfrac{1}{2}=-\dfrac{9}{2}\end{matrix}\right.\)

\(372-19\cdot4+981:19-13\)

=372-76+981/19-13

\(=283+\dfrac{981}{19}=\dfrac{6358}{19}\)

Bạn làm 2 Trg họp thôi
x- 15= 0 x =15
2x-16=0 x=8

ta có 2 trương hợp

th1 x-15 =0

x=0+15

x=15

th2

2x-16=0

2x=16

x=8

Hình ảnh "quê hương là vòng tay ấm" cho thấy quê hương ko có j sánh bằng. Quê hương như một luồng gió ấm thổi qua khiến chúng ta cảm thấy thật yên bình. Nói "quê hương là vòng tay ấm" vì khi chúng ta buồn,  chúng ta thất bại, chúng ta thành công, thì nơi nên đến đầu tiên chính là quê hương. Tác giả đã cho thấy lòng yêu quê hương thắm thiết và muốn thể hiên qua câu thơ ấy. 

Mik tự nghĩ nhé ko lấy trên mạng đâu nên bn ko lo bị trùng!