a) -1 - 2 - 3 - ..... - 200 = - (1 + 2 + 3 + .... + 200)
Numarul de termeni = (ultimul termen - primul termen) : ratie + 1
Nr T = (200 - 1) : 1 + 1
Nr T = 199 + 1
Nr T = 200
Suma = (ultimul termen + primul termen) × numarul de termeni : 2
S = (200 + 1) × 200 : 2
S = 201 × 100
S = 20100
b) - 3 - 6 - 9 - ..... - 501 = - (3 + 6 + 9 + .... + 501)
Nr T = (501 - 3) : 3 + 1
Nr T = 498 : 3 + 1
Nr T = 166 + 1
Nr T = 167
S = (501 + 3) × 167 : 2
S = 504 : 2 × 167
S = 252 × 167
S = 42084
c) -2 - 4 - 6 - ... - 324 = - (2 + 4 + 6 + ... + 324)
Nr T = (324 - 2) : 2 + 1
Nr T = 322 : 2 + 1
Nr T = 161 + 1
Nr T = 162
S = (324 + 2) × 162 : 2
S = 326 × 81
S = 26406
d) -1 - 5 - 9 - .... - 405 = - (1 + 5 + 9 + ... + 405)
Nr T = (405 - 1) : 4 + 1
Nr T = 404 : 4 + 1
Nr T = 101 + 1
Nr T = 102
S = (405 + 1) × 102 : 2
S = 406 × 51
S = 20706
