Question

Tìm x thuộc N biết:

a. x+(x+1)+(x+2)+(x+3)+...+(x+30)=1240

b. 1+2+3+...+x=210

Answer 1

a) x+(x+1)+(x+2)+…+(x+30)=1240

=>x+x+1+x+2+x+3+…+x+30=1240

=>x+x+x+…+x+1+2+3+…+30=1240

Từ 1->30 có: (30-1):1+1=30(số)

=>31.x+(30+1).30:2=1240

=>31.x+31.15=1240

=>31.x+465=1240

=>31.x=1240-465

=>31x=775

=>x=775:31

=>x=25

b) 1+2+3+…+x=210

=>x.(x+1):2=210

=>x.(x+1)=420

=>x.(x+1)=20.21=20.(20+1)

=>x=20

Answer 2

Bài 1:

a,x + ( x + 1) + (x + 2) + (x + 3) +....+ (x + 30) = 1240

x + x +x +.... + x + (1 + 2+ 3+ ....+ 30) = 1240

31x + 465 =1240

31x = 1240 - 465

31x = 775

x = 775 : 31

x = 25

b, 1+2+3+...+x=210

\(\frac{x.\left(x+1\right)}{2}=210\)

x(x+1)=210.2

x(x+1)=420

x(x+1)=20.21

=>x=20

Answer 3

BAi 1:

x + (x+1) + (x+2) + (x+3) + ...+ (x+30) = 1240

x + x + x +...+ x + 1 + 2 + 3 + 4 +..........+ 30 =1240

day so 1 + 2 + 3 + ... + 30 co so so hang la:

(30-1):1+1=30

Answer 4

vay co 31 so x

Co: 31.x + (30+1).30:2=1240

31.x+465=1240

31.x=1240-465

31.x=775

x=20

vay x=20

Answer 5

1.x=25 2.x=20

Answer 6

(x+1)+(x+2)+(x+3)+...+(x+30)=525

Answer 7

toan 6 ak

Answer 8

30 bạn nhé

Answer 9

a) Ta có : x+(x+1)+(x+2)+(x+3)+...+(x+30)=1240

=>31x+(1+2+3+...+30)=1240

=>31x+465=1240

=>31x=1240-465=775

=>x=775:31=25

Vậy x=25