Question

[Nguyễn Thuỳ Linh]

giải nhanh giúp mik nhé !

Answer 1

[Minh Vo Nhat]

Đặt biểu thức trên bằng A

=> 5A = 5 x ( \(\frac{1}{11x16}\)+ \(\frac{1}{16x21}\)+ .... + \(\frac{1}{61x66}\))

= \(\frac{5}{11x16}\)+ \(\frac{5}{16x21}\)+ .... + \(\frac{5}{61x66}\)

= \(\frac{16-11}{11x16}\)+ \(\frac{21-16}{16x21}\)+ ... + \(\frac{66-61}{61x66}\)

= \(\frac{1}{11}\)- \(\frac{1}{16}\)+ \(\frac{1}{16}\)- \(\frac{1}{21}\)+ .... + \(\frac{1}{61}\)- \(\frac{1}{66}\)

5A = \(\frac{1}{11}\)- \(\frac{1}{66}\)

A = ( \(\frac{1}{11}\)- \(\frac{1}{66}\)) : 5

A = \(\frac{1}{66}\)

Answer 2

[𝚃̷ ❤𝚇̷❤ 𝙷̷]

TL

A=1/66

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