Question

1+3+5+......................+x = 501501

tim x

Answer 1

Ta có: 5 = 2+3; 9 = 4+5 ; 13 = 6+7 ; 17 = 8+9;.....

Do vậy x = a + ( a + 1)  ( a thuộc N )

Nên 1 + 5 + 9 + 13 + 16 + ....+ x = 1+2+3+4+5+6+7+.....+a+ ( a + 1 ) = 501501

Hay (a + 1)( a + 2)  = 1003002 = 1001 . 1002 

Suy ra : a = 1000

Do đó : x = 1000 + ( 1000+ 1) = 2001

Answer 2

VICTOR_Nobita Kun:ngu vậy, đề là x sao là a =>copy

Answer 3

1+5+9+13+17+...+x=501501

(x+1)[(x-1):4+1]:2=501501

(x+1)[(x-1).1/4+1].1/2=501501

(x+1)(1/4x-1/4+1).1/2=501501

[(x+1).1/4x-(x+1).1/4+(x+1)].1/2=501501

[(x+1)(-1/4+1)+(x+1).1/4x].1/2=501501

[(x+1).3/4+(x+1).1/4x].1/2=501501

(x+1)(3/4+x/4).1/2=501501

(x+1)[(3+x)/4] .1/2=501501

(x+1)[(3+x)/8] =501501

[(x+1)(3+x)]/8=501501

(x+1)(3+x)=4012008

3x+x^2+3+x=4012008

x^2+4x+3=4012008

x^2+x+3x+3=4012008

x(x+1)+3(x+1)=4012008

(x+1)(x+3)=4012008

(x+1)(x+3)=2002.2004

suy ra x+1=2002 và x+3=2004

           x=2001     ; x=2001

vậy x=2001