Question

Tính bằng cách thuận tiện nhất 

3 / 1*2 + 3/2*3 + 3/3*4 + 3/4*5 + 3/5*6

 

Answer 1

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Answer 2

3/1*2 + 3/2*3 + 3/3*4 + 3/4*5 + 3/5*6

= 3 * ( 1/1*2 + 1/2*3 + 1/3*4 + 1/4*5 + 1/5*6 )

= 3 * (1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/5 - 1/5 - 1/6)

= 3 * (1/1 - 1/6)

= 3 * 5/6 

= 5/2 

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Answer 3

Dấu "." tức là dấu "x" nha bạn.

\(\frac{3}{1.2}+\frac{3}{2.3}+\frac{3}{3.4}+\frac{3}{4.5}+\frac{3}{5.6}\)

\(=3\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}\right)\)

\(=3\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{5}-\frac{1}{6}\right)\)

\(=3\left(1-\frac{1}{6}\right)\)

\(=3.\frac{5}{6}\)

\(=\frac{5}{2}\)