a 1/30+2/42+3/56+.....+4/380
b 3-5+7-9+.....+143-145+147
tính thuận tiện
a ( 145 * 99 - 145 ) - ( 143 * 101 - 143 )
b ( 500 * 9 - 250 * 18 ) * ( 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 +9 )
c ( 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 ) * ( 6 * 8 - 48)
a) N = 1/2 + 1/6+ 1/12 + 1/20 + 1/30 +1/42 + 1/56 + 1/72 +1/90
b) 5/8 + 2/9 -2/5 + 3/8 + 4/9 + 1/3 - 3/5 =
c) 4 1/5 + 5 1/3 - 2 2/3 x 3 1/5 + 9/25 : 9/20 =
a, 2/1×3×2 + 2/3×5×2 × 2/5×7×2 + 2/7×9×2 2/9×11×2 2/11×13×2
b, 5/1×2 + 5/2×3 + 5/3×4 + ......+ 5/28×29
c, 4/2×4 + 4/4×6 +......+4/28×30
d, 4/6 + 4/12 + 4/20 + 4/40 + 4/42 + 4/56
Các bạn giải rõ hộ mình nha
Tinh hon so sau :
1 1/2 +2 1/6 + 3 1/12 + 4 1/20 + 5 1/30 + 6 1/42 + 7 1/56 + 8 1/72 +9 1/90 +1/10
a) 1/2+1/3+1/4+1/5+...+1/9+1/10
b) 1/12+1/20+1/30+1/42+1/56+1/72+1/90
Tính nhanh tổng:
a, S=1 - 1/5 +7/12 -9/20 + 11/30 - 13/42 + 15/56 + 19/90 - 21/110 + 23/132
b, P=21 * (4/1*3 - 8/3*5 + 12/5*7 - 16/7*9 + ... + 36/17*19 - 40/19*21 ( dấu * là dấu nhân nhé)
B= 3/2-5/6+7/12-9/20+11/30-13/42+15/56-17/72
3/2 - 5/6+ 7/12- 9/20 +11/30-13/42 +15/56 - 17/72+ 19/90
