Question

Tính nhanh

A= 3/4+3/28+3/70+3/130+3/208+3/304

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Answer 1

A=\(\frac{3}{4}+\frac{3}{28}+\frac{3}{70}+\frac{3}{130}+\frac{3}{208}+\frac{3}{304}\)

A= \(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+\frac{3}{13.16}+\frac{3}{16.19}\)

A= \(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{17}+\frac{1}{17}-\frac{1}{19}\)

A= 1 - \(\frac{1}{19}\)

A= \(\frac{18}{19}\)

Answer 2

X=3/4+3/28+...+3/304

X=3/1x4+3/4x7+....+3/13x16

X=1-1/4+1/4-1/7+....+1/13-1/16

X=1-1/16

X=15/16

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Answer 3

A=3/4+3/28+3/70+3/130+3/208+3/304

  =3/1x4+3/4x7+3/7x10+3/10x13+7/13x16+7/16x19

  =3/1-3/4+3/4-3/7+3/7-3/10+3/10-3/13+3/13-3/16+3/16-3/19

  =3/1-3/19=57/19-3/19=54/19

Answer 4

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