Question

[itsuka kotori]

A=1/7+1/91+1/247+...+1/1147

Answer 1

[Bùi Thế Hào]

A=\(\frac{1}{1.7}+\frac{1}{7.13}+...+\frac{1}{31.37}\)= \(\frac{1}{6}.\)(\(\frac{6}{1.7}+\frac{6}{7.13}+...+\frac{6}{31.37}\))=\(\frac{1}{6}.\)(\(\frac{1}{1}-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+...+\frac{1}{31}-\frac{1}{37}\)) = \(\frac{1}{6}.\left(\frac{1}{1}-\frac{1}{37}\right)=\frac{1}{6}.\frac{36}{37}=\frac{6}{37}\)

ĐS: A=6/37

Answer 2

[Đàm Ngọc Luyện]

em làm như sau nhé : :))) 

6A= 6/7 + 6/91+...+ 6/1147

<=>6A= 6/7+1/7-1/13+1/13-1/19+...+1/31-1/37

<=> 6A= 6/7+1/7 -1/37

<=> A=6/37