B = 1/30 + 1/42 + 1/56 + 1/72 + 1/90 + 1/110 + 1/132 + 1/156
B = 1/5x6 + 1/6x7 + 1/7x8 + 1/8x9 + 1/9x10 + 1/10x11 + 1/11x12 + 1/12x13
B = 1/5 -1/6 + 1/6- 1/7 + 1/7 -1/ 8 + 1/8 -1/9 +1/9 -1/10 + 1/10 - 1/11 + 1/11-1/12 +1/12 -1/13
B = 1/5 - 1/13
B = 8/65
B=1/30+1/42+1/56+1/72+1/90+1/110+1/132+1/156
Tính 1/20 + 1/30 + 1/42 + 1/56 + 1/ 72 + 1/90 + 1/110 + 1/ 132 + 1/156
A = 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 + 1/ 110 + 1/132 + 1/156
1/30+1/42+1/56+1/72+1/90+1/110+1/132=21/x
tính nhanh
1/20+1/30+1/42+1/56+1/72+1/90+1/110+1/132
Tính nhanh:
1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 + 1/110 + 1/132
Tính nhanh
\(\dfrac{1}{20}\)+\(\dfrac{1}{30}\)+\(\dfrac{1}{42}\)+\(\dfrac{1}{56}\)+\(\dfrac{1}{72}\)+\(\dfrac{1}{90}\)+\(\dfrac{1}{110}\)+\(\dfrac{1}{132}\)
=
1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/110+1/132
Giải ra cho mình nhé
tính tổng sau bằng cách hợp lí
10,9-10,4+10,3-9,8+9,7-9,2+9,1....-3,8+3,7-3,2=
\(\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}+\frac{1}{132}+\frac{1}{156}=\)
