( 2x + 1 ) + ( 2x + 2 ) + ... + ( 2x + 2015 )
<=> ( 2x + 2x + 2x + .... + 2x ) + ( 1 + 2 + 3 + .... + 2015 ) = 0
<=> ( 2x . 2015 ) + [ 2015 . ( 2015 + 1 ) ] : 2 = 0
<=> 4030x + 2031120 = 0
<=> 4030x = - 2031120
<=> x = - 2031120 : 4030
=> x = - 504
Vậy x = - 504