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Ta có : S1 = 2-4+6-8+10-12+.........+1998-2000 = (2-4)+(6-8)+(10-12)+..........+(1998-2000) 

= -2 + (-2)+(-2)+..........+(-2)   = -2 . 500 = -1000

Vậy S1 = -1000

(x+2)(y-3)=5

=>x+2=5

x=5-2

x=3

=>y-3=5

y=5+3

y=8

9,25

giải 

tổng 3 số là

(8,5*2+8,1*2+7,35*2)/2=23,95

số thứ nhất là

23,95-8,5*2=6,95

số thứ 2 là

23,95-8,1*2=7,75

số thứ 3 là

23,95-7,75-6,95=9,25

số lớn nhât là 9,25

x(y-1)+2(y-1)-5=0
(x+2)(y-1)=-5
Vì x+2>0 => y-1<0
Mà y thuộc N => y-1 =-1=> y=0
x+2=5=>x=3

Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that is closest in meaning to each of the following questions.

"If I were you, I'd ask the teacher for help" he said.

A. He suggested asking the teacher for help.

B. He said if he was me, he would ask the teacher for help.

C. He advised me to ask the teacher for help.

D. He told me that he'd ask the teacher for help.

Of the two sisters, Thuy Kieu is the _______ .

A. eldest

B. elder

C. eldly

D. most eldly