Tìm x biết :
a) 1 + 2 + 3 + ..... + x = 210
b) 1 + 3 + 5 + ..... + ( 2 . x - 1 ) = 225
c) 2 + 4 + 6 +........ + 2 . n = 210
1 + 2 + 3 + .......+ ( x +1 ) + x = 210
tìm x
timf x-210=-1+-2+-3+....+(-x+1)+(-x) vay x=
-210 = ( - 1 ) + ( - 2 ) + ( - 3 ) + . . . + ( - x + 1 ) + ( - x )
Tìm x biết:-210=(-1)+(-2)+(-3)+...+(-x+1)+(-x)
tìm x :-210 = (-1) + ( -2) + (-3) +.............+( -x-1) +(-x)
a) x + (x + 1) + (x + 2) + (x+3)+...+(x + 30) = 1240
b) x + 1 + 2 + 3 + ... + x = 210
-210= -1 + -2 +-3 +...+ (-x-1) + (-x)
Tìm x
-210=(-1)+(-2)+(-3)+...+(-x+1)+x
