1)Ta có:S=\(n_1^2+n_2^2+...+n_{10}^2\)=\(\left(n_1+n_2+...+n_{10}\right)^2-2.\left(n_1n_2+n_2n_3+.....+n_{10}.n_1\right)=2013^2-2.\left(n_1n_2+n_2n_3+.....+n_{10}.n_1\right)\)

Do 2013² chia 2 dư 1

\(2.\left(n_1n_2+n_2n_3+.....+n_{10}.n_1\right)\) chia hết cho 2

=>\(2013^2-2.\left(n_1n_2+n_2n_3+.....+n_{10}.n_1\right)-1\) chia hết cho 2

=>S-1 chia hết cho 2

Tâm trạng thật, mk cũng có tâm trạng gần như thế này

a)Xét tứ giác AEDF có: DE//AB, DF//AC

\(\Rightarrow\)AEDE là hình bình hành

b) Vì 2 đường chéo của hình bình hành cắt nhau tại trung điểm mỗi đường nên IA=ID, IF=IE suy ra E đối xứng với F qua I

a) \(x^2-10x+16=x^2-8x-2x+16=\left(x^2-8x\right)-\left(2x-16\right)=x\left(x-8\right)-2\left(x-8\right)=\left(x-8\right)\left(x-2\right)\)b) \(x^2-2x-15=x^2+3x-5x-15=\left(x^2+3x\right)-\left(5x+15\right)=x\left(x+3\right)-5\left(x+3\right)=\left(x+3\right)\left(x-5\right)\)c) \(2x^2+7x+3=2x^2+x+6x+3=\left(2x^2+x\right)+\left(6x+3\right)=x\left(2x+1\right)+3\left(2x+1\right)=\left(2x+1\right)\left(x+3\right)\)

e) \(25-x^2+4xy-4y^2=5^2-\left[x^2+4xy-\left(2y\right)^2\right]=5^2-\left(x-2y\right)^2=\left(5-x+2y\right)\left(5+x-2y\right)\)

f) \(x^4-4x^3+4x^2=x^2\left(x^2-4x+4\right)=x^2\left(x^2-4x+2^2\right)=x^2\left(x-2\right)^2\)

g) \(x^3-x^2-x+1=\left(x^3-x^2\right)-\left(x-1\right)=x^2\left(x-1\right)-\left(x-1\right)=\left(x-1\right)\left(x^2-1\right)\)

h) \(a^5+27a^2=a^2\left(a^3+27\right)=a^2\left(a^3+3^3\right)=a^2\left(a+3\right)\left(a^2-3a+9\right)\)

i) \(x^3+3x^2-3x-1=\left(x^3-1\right)+\left(3x^2-3x\right)=\left(x-1\right)\left(x^2+x+1\right)+3x\left(x-1\right)=\left(x-1\right)\left(x^2+x+1+3x\right)=\left(x-1\right)\left(x^2+4x+1\right)\)k) \(4a^2b^2-\left(a^2+b^2-1\right)^2=\left(2ab\right)^2-\left(a^2+b^2-1\right)^2=\left(2ab-a^2-b^2+1\right)\left(2ab+a^2+b^2-1\right)=\left[-\left(a+b\right)^2+1\right]\left[\left(a+b\right)^2-1\right]\)

\(=\left[1-\left(a+b\right)^2\right]\left[\left(a+b\right)^2-1\right]=\left(1-a-b\right)\left(1+a+b\right)\left(a+b-1\right)\left(a+b+1\right)=\left(a+b+1\right)^2\left(1-a-b\right)\left(a+b-1\right)\)

??? 

1) I drank two glasses of milk for breakfast this morning ( how many)

How many glasses of milk did you drink for breakfast this morning?

2) they built a new scholl two years ago (when)

When did they build a new school?

3) we ate lunch at the canteen with ourfriends today. (where)

Where did you eat lunch with your friends today?

4) Mai took an english course lát summer. (What course)

What course did Mai take last summer?

5) THey found Mrs. green's purse under the seat. (where)

Where did they find Mrs. Green's purse?

1) You made five mistakes in your last writing. (How many?)

-How many mistakes did I make in my last writing?

2) Mr. Stevens told his students the answers to the problems. (What?)

-What did Mr, Stevens tell his students?

3) She went to the concert last night. (Where?)

-Where did she go last night?

4)My uncle sold his old house last year. (What?)

-What did your uncle sell last year?

Nick j vậy bn? Bạn có nick này r đấy thôi