C=1-2-3+4+5-6-7+8+...-297-298-299+300+301
=(1-2-3+4)+(5-6-7+8)+...+(297-298-299+300)+301 (75 cặp)
= 0 + 0 +...+ 0 +301 (75 chữ số 0)
= 301
Vậy C=301
Tính hợp lí
1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + ... + 297 + 298 - 299 - 300 +301
Help
:'(
tinh nhanh 1-2-3+4+5-6-7+...+297-298-299+300+301-302-303+304+305
A = 1+2+3-4-5-6+7+8+9-10-11-12+.....+ 295+ 296 + 297 - 298 - 299 - 300 + 301
tinh A
tính:
1+2-3-4+5+6-7-8+...+297+298-299-300
1+2-3-4+5+6-7-8+....+298-299-300+301+302
1+2-3-4+5+6-7-8+9+10-11-12+........+298-299-300+301+302 = ?
tính bằng cách hợp lý:
a) (1981.1982-990):(1980.1982+992)
b) 302+301-300-299+298+297-296-295+...+6+5-4-3+2+1
Tinh nhanh: M=1+2-3-4+5+6-7-8+9+10-11-12+...+...298-299-300+301+302
tính tổng A
A= 1+2-3-4+5+6-7-8+9+10-11-12+.........+298-299-300+301
