Ta có:\(\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+...+\frac{1}{210}\)
\(=\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+....+\frac{1}{14.15}\)
\(=\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{14}-\frac{1}{15}\)
\(=\frac{1}{6}-\frac{1}{15}=\frac{1}{10}\)
tinh:1/42+1/56+1/72+1/90+1/110+1/132+1/156+1/182+1/210
A=1/42+1/56+1/72+1/90+1/110+1/156+1/182+1/210
A=1/42+1/56+1/72+1/90+1/110+1/132+1/156+1/182+1/210
Tinh hop ly tong sau
\(A=\frac{-1}{20}+\frac{-1}{30}+\frac{-1}{42}+\frac{-1}{56}+\frac{-1}{72}+\frac{-1}{90}\)
Tinh tong:
S1=1/2+ 1/6+ 1/12+ 1/20 + 1/30 + 1/42 + 1/56+ 1/72 +1/90.
Giup mk vs nhe ,mk se tick.
tinh tong A=1-5/6+7/12-9/20+11/30-13/42+15/56-17/72+19/90
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 GIA TRI BIEU THUC :A=1/30+1/42+1/56+1/72+1/90+1/110+1/132
Tinh gia tri cua A:
A=1/30+1/42+1/56+1/72+1/90+1/110+1/132
