Tính hợp lí:
a) A = \(\dfrac{1}{56}\) + \(\dfrac{1}{72}\) + \(\dfrac{1}{90}\) + \(\dfrac{1}{110}\) + \(\dfrac{1}{132}\) + \(\dfrac{1}{156}\) ;
b) B = \(\dfrac{4}{21}\) + \(\dfrac{4}{77}\) + \(\dfrac{4}{165}\) + \(\dfrac{4}{285}\) +\(\dfrac{4}{437}\) +\(\dfrac{4}{621}\);
c) C = \(\dfrac{1}{21}\) + \(\dfrac{1}{77}\) +\(\dfrac{1}{165}\) +\(\dfrac{1}{285}\) +\(\dfrac{1}{437}\) +\(\dfrac{1}{621}\) ;
d) D = \(\dfrac{1}{1.6}\) + \(\dfrac{1}{6.11}\) +\(\dfrac{1}{11.16}\) +\(\dfrac{1}{16.21}\) +\(\dfrac{1}{26.31}\) .
tính tổng
S=1/56+1/72+1/90+1/110+1/132+1/156
A=1/42+1/56+1/72+1/90+1/110+1/132+1/156+1/182+1/210
1/20+1/30+1/42+1/56+1/72+1/90+1/110+1/132+1/156 = ?
tinh:1/42+1/56+1/72+1/90+1/110+1/132+1/156+1/182+1/210
Tính tổng A= 1- 5/6 +7/12 - 9/20 + 11/30 - 13/42 + 15/56 - 17/72 + 19/90 - 21/110 + 23/132 - 25/156
tính hợp lý
,A=\(\frac{1}{56}\)+\(\frac{1}{72}\)+\(\frac{1}{90}\)+\(\frac{1}{110}\)+\(\frac{1}{132}\)+\(\frac{1}{156}\)
\(A=\frac{1}{5}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}+\frac{1}{132}+\frac{1}{156}\)
tính \(\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}+\frac{1}{132}+\frac{1}{156}\)
1/56+1/72+1/90+1/110+1/132+1/156+1/182+1/210+1/240
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