a,x+(x+1)+(x+2)+...+(x+30)=1240
<=>31x+(30+1).30:2=1240
<=>31x+465=1240
<=>31x=775
<=>x=25
b,1+2+3+....+x=210
=>x(x+1):2=210
<=>x(x+1)=420=20.21
=>x=20
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tim x thuoc N biet
x+(x+1)+(x+2)+(x+3)+.......+(x+30)=1240
1+2+3+.....+x=210
tim x thuoc z biet 1+2+3+...+x=210
1 )Tim x, y thuoc Z
x + y = x.y
2) Tim x thuoc Z
(x + 1)+(x+3)+(x+5)+...+(x+99)=0(x-3)+(x-2)+(x-1)+...+10+11=11-12(x-5)+7(3-x)=530(x+2)-6(x-5)-24x=100tim X thuon N ,biet :
a,x+(x+1)+(x+2)+........+(x+30)=1240
b, 1+2+3+4+........+ x =210
tim x thuoc z ,biet x+(x+1)+(x+2) +...+(x+30)=1240
TIM x THUOC Z , BIET :
a) / 2x + 1 / = 7
b) 3/x + 1 / + 1 = 27
c) 20 = 20 + 19 + 18 + 17 + ..... + x
d) x + ( x+ 1 ) + ( x + 2 + ...... + 29 + 30 = 30
tim x
6 chia het cho ( x - 1)
x thuoc Ư (30) và x > 12
8 chia het cho x
14 chi het cho (2 . x + 3)
tim x thuoc z
(x3+5)(x2+10)(x2+15)(x3+30)
Tim x thuoc Z: (x+1)+(x+2)+(x+3)+...+(x+40)=1000