Question

Tính nhanh:

\(\frac{1}{1x4}+\frac{1}{4x7}+\frac{1}{7x10}+...+\frac{1}{97x100}\)

Answer 1

1/1*4 + 1/4*7 + 1/7*10 + ... + 1/97*100

= 1/3(3/1*4 + 3/4*7 + 3/7*10 + ... + 3/97*100)

= 1/3(1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 + .... + 1/97 - 1/100)

= 1/3(1 - 1/100)

= 1/3*99/100

= 33/100

Answer 2

trả lời 

=33/100

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