1/2 + 1/6 + 1/12 + 1/20 + 1/30
= 1/1×2 + 1/2×3 + 1/3×4 + 1/4×5 + 1/5×6
= 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6
= 1 - 1/6
= 5/6
Tính
1. A= 1/2+1/6+1/12+/1/20+1/30+1/42+1/56
2. B = 3/2+5/6+7/12+-9/20+11/30-13/42+15/56
Tập hợp ước số của số 60 là:
A. Ư(60) = {1; 2; 3; 5; 12; 20; 30; 60}
B. Ư(60) = {1; 2; 3; 4; 15; 20; 30; 60}
C. Ư(60) = {1; 2; 3; 4; 5; 12; 15; 20; 30; 60}
D. Ư(60) = {1; 2; 3; 4; 5; 6; 10; 12 15; 20; 30; 60}
`x−1/2−1/6−1/12−1/20=1/30`
1/2 + 1/6 + 1/12 + 1/20 + 1/30
1/2 + 1/6 +1/12 +1/20 + 1/30 +1/42+ 1/56
Tính nhanh
1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42
1/2+1/6+1/12+1/20+1/30+...+1/9900
1/2+1/6+1/12+1/20+1/30+1/42
1/2+1/6+1/12+1/20+1/30+...+1/420
