A=\(\frac{1}{42}+\frac{1}{56}+..............+\frac{1}{210}\)
=\(\frac{1}{6.7}+\frac{1}{7.8}+............+\frac{1}{14.15}\)
=\(\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+............+\frac{1}{14}-\frac{1}{15}\)
=\(\frac{1}{6}-\frac{1}{15}\)
=\(\frac{1}{10}\)
A=1/42+1/56+1/72+1/90+1/110+1/132+1/156+1/182+1/210
tinh:1/42+1/56+1/72+1/90+1/110+1/132+1/156+1/182+1/210
1/56+1/72+1/90+1/110+1/132+1/156+1/182+1/210+1/240
giúps mình với mình đang cần gấp
tinh tong: 1/42+1/56+1/72+1/90+...+1/182+1/210
1/20+1/30+1/42+1/56+1/72+1/90+1/110+1/132+1/156 = ?
\(A=\frac{1}{5}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}+\frac{1}{132}+\frac{1}{156}\)
tính \(\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}+\frac{1}{132}+\frac{1}{156}\)
A=-1/20+-1/30+-1/42+-1/56+-1/72+-1/90+-1/110+-1/132
A=1/30+1/42+1/56+1/72+1/90+1/110+1/132
