C=1-2-3+4+5-6-7+8-...-297-298-299+300+301
Tính hợp lí
1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + ... + 297 + 298 - 299 - 300 +301
\(=\left(1+2-3-4\right)+\left(5+6-7-8\right)+...+\left(297+298-299-300\right)+301\)
\(=\left(-4\right)+\left(-4\right)+...+\left(-4\right)+301\)
\(=301-4\cdot75=301-300=1\)
Tính \(S=1+2-3-4+5+6-7-8+...+297+298-299-300+301+302\)
B = 1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + 9 + 10 - 11 - 12 + ... - 299 - 300 + 301 + 302 (có 302 số; 302 chia 4 dư 2)
B = 1 + (2 - 3 - 4 + 5) + (6 - 7 - 8 + 9) + (10 - 11 - 12 + 13) + ... + (298 - 299 - 300 + 301) + 302
B = 1 + 0 + 0 + 0 + ... + 302
B = 1 + 302
B = 303
Chúc bn hc tốt
Tính hợp lí
1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + ... + 297 + 298 - 299 - 300 +301
Help
:'(
1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + ... + 287 + 298 - 299 - 300 + 301
= 1 + (2 - 3 - 4 + 5) + (6 - 7 - 8 + 9) + ... + (298 - 299 - 300 + 301)
= 1 + 0 + 0 + ... + 0
= 1
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 +.............+297+298-299-300
= (1+2)-(3+4)+(5+6-(7+8)+.........+(297+298)-(299+300)
=3-7+11-15+.......+595-599
= (3+11+......+595)-(7+15+...........+599)
=22425-22725
= (-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 = ?
1+2-3-4+5+6-7-8+9+10-11-12+........+298-299-300+301+302 =
1+2+(5-3)+(6-4)+(9-7)+(10-8)+…….+(301-299)+(302-300)=
Từ 302 đến 3 có số cặp là [(302-3):1+1]:2=150 cặp. Mà mỗi cặp có giá trị là 2
Vậy 1+2-3-4+5+6-7-8+9+10-11-12+........+298-299-300+301+302 =
1+2+2×150=3+300=303
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