Question

1-2-3-4-5-...-97-98-99=?

Answer 1

we use the sum of an arithmetic formula
1 -2 -3 - 4 -5 ....-96 - 97 - 98 - 99 = 1 + Sn


`S_(n) = ( a_(1) + a_(n) )/(2) * n`

n = 98 (-2, -3,......98, -99)
a₁ = -2
a₉₈ = -99


`S_(98) = (-2 + (-99))/(2) * 98 = (-101)/(2) * 98 = -50,5 *98 = 4949 \\ \\ 1 - 4949 = -4948`

Answer - 4948