Gauss:
1 + 2 + 3 + ... + n = n ( n + 1 ) : 2
x = ( 1 + 2 + 3 + ... + 98 ) + 49
x = [ 98 × ( 98 + 1 ) : 2 ] + 49
x = ( 98 × 99 : 2 ) + 49
x = ( 9 702 : 2 ) + 49
x = 4 851 + 49
x = 4 900
X=98×99:2+49
X=9702:2+49
X=4851+49
X=4900
