2F = 2/10 x 12 + 2 / 12 x 14 + 2 / 14 x 16 + ... + 2 / 108 x 110
= 1/10 - 1/12 + 1/12 - 1/14 + 1/14 - 1/16 + ... + 1/108 -1/110
= 1/10 - 1/110
= 1/11
E=2/10×12+2/12×14+2/14×16+.............+2/108×110
Tính nhanh:
A = 1/10 + -1/11 + 1/12 + -1/13 + 1/14 + -1/15 + 1/16 +1/15 + -1/14 + 1/13 + -1/12 + 1/11 + -1/10
1/2+1/4+1/6+1/8+1/10+1/12+1/14+1/16+1/18+1/20=?
Tính. 1/2+5/6+11/12+.....+89/90+108/110+10/11
tính tổng đại số sau
a)2-4+6-8+...+1998-2000
b)11-12+13-14+15-16+17-18+19-20
c)101-102-(-103)-104-(-105)-106-(-107)-108-(-109)-110
1 + 2 + 3 + ... + 99 + 100
2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18
1 + 2 + 3 + 4 + ... + 200
1+[2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17]*0,000001
1+2-3-4+5+6-7-8+9+10-11-12+13+14-15-16+...+301+302
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20=?
