Question

Tính cách thuận tiện nhất

a15 x\(\dfrac{2121}{4343}\) +15x\(\dfrac{22222}{434343}\)

b\(\dfrac{16x25+44x100}{29x96+142x48}\)

c\(\dfrac{399x45+55x399}{1995x1996-1991x1995}\)

d\(\dfrac{1}{2x3}\)+\(\dfrac{1}{3x4}\) +\(\dfrac{1}{4x5}\)+\(\dfrac{1}{5x6}\)

Answer 1

`a) 15 xx 2121/4343 + 15 xx 222222/434343`

`= 15 xx ( 2121/4343 + 222222/434343)`

`= 15 xx (212121/434343 + 222222/434343)`

`= 15 xx 434343/434343`

`= 15 xx 1`

`= 15`

`b) (16 xx 25 + 44 xx 100)/(29 xx 96 + 142 xx 48)`

`=` \(\dfrac{4\times4\times25+4\times11\times100}{29\times12\times8+2\times12\times4\times71}\)

\(=\dfrac{400\times\left(1+11\right)}{12\times8\times\left(29+71\right)}\)

\(=\dfrac{400\times12}{12\times8\times100}\)

\(=\dfrac{4\times100\times12}{12\times4\times2\times100}=\dfrac{1}{2}\)

`c)(399xx 45+55xx399)/(1995xx1996-1991xx1995)`

`=` `(399 xx (45+55))/(1995 xx (1996-1991) )`

`=` `(399 xx 100)/(1995xx4)`

`=` `4`

`d)` \(\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+\dfrac{1}{4\times5}+\dfrac{1}{5\times6}\)

`= 1/2 -1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6`

`= 1/2 - 1/6`

`= 1/3`

Answer 2

d) = 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6

= 1/2 - 1/6

= 1/3

 

Answer 3

d) = 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6

= 1/2 - 1/6

= 1/3