\(\dfrac{1}{3}+\dfrac{1}{15}+\dfrac{1}{25}+\dfrac{1}{35}+\dfrac{1}{63}+\dfrac{1}{99}+\dfrac{1}{143}\)

\(=\left(\dfrac{2}{1\cdot3}+\dfrac{2}{3\cdot5}+\dfrac{2}{5\cdot7}+\dfrac{2}{7\cdot9}+\dfrac{2}{9\cdot11}+\dfrac{2}{11\cdot13}\right)\cdot\dfrac{1}{2}+\dfrac{1}{25}\)

\(=\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-...+\dfrac{1}{11}-\dfrac{1}{13}\right)\cdot\dfrac{1}{2}+\dfrac{1}{25}\)

\(=\left(1-\dfrac{1}{3}\right)\cdot\dfrac{1}{2}+\dfrac{1}{25}\)

\(=\dfrac{2}{3}\cdot\dfrac{1}{2}+\dfrac{1}{25}\)

\(=\dfrac{1}{3}+\dfrac{1}{25}\)

\(=\dfrac{28}{75}\)

cám ơi bạn

cảm ơn bạn rất nhiều

24 . 25 + ( 4 . 6 ) . 37 + 24 . 38

24 . 25 + 24 . 37 + 24 . 38

24 . ( 25 + 37 + 38 )

24 . 100 

2400

24 . 25 + 4 . 37 . 6 +24 . 38

= 24 . 25 + 24 . 37 + 24 . 38

= 24 . ( 25 + 38 + 37 )  

= 24 . 100 = 2400

a, =46x(-217+117) =46x(-100)=-4600

b, =-25x(78-28)=-25x50=-1250

c,=35(-63-23)=35x(-86)=3010

a -> c => máy tính

cách tình nhanh và gọn nhất là bấm máy tính ư

\(\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+....+\frac{2}{575}+\frac{2}{675}\)

\(=\frac{2}{3\times5}+\frac{2}{5\times7}+\frac{2}{7\times9}+...+\frac{2}{23\times25}+\frac{2}{25\times27}\)

\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{23}-\frac{1}{25}+\frac{1}{25}-\frac{1}{27}\)

\(=\frac{1}{3}-\frac{1}{27}=\frac{8}{27}\)

Vậy ....

\(\frac{2}{15}+\frac{2}{35}+\frac{2}{69}+........+\frac{2}{575}+\frac{2}{675}\)

\(=\frac{2}{3\times5}+\frac{2}{5\times7}+........+\frac{2}{23\times25}+\frac{2}{25\times27}\)

\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+.......+\frac{1}{23}-\frac{1}{25}+\frac{1}{25}-\frac{1}{27}\)

\(=\frac{1}{3}-\frac{1}{27}\)

\(=\frac{8}{27}\)

\(\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+\frac{2}{99}+...+\frac{2}{575}+\frac{2}{675}\)

\(=\frac{2}{3\times5}+\frac{2}{5\times7}+\frac{2}{7\times9}+\frac{2}{9\times11}+...+\frac{2}{23\times25}+\frac{2}{25\times27}\)

\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{23}-\frac{1}{25}+\frac{1}{25}-\frac{1}{27}\)

\(=\frac{1}{3}-\frac{1}{27}\)

\(=\frac{8}{27}\)

_Chúc bạn học tốt_

=(1-1/2)(1+1/2)*...*(1+1/10)(1-1/10)

=1/2*2/3*...*9/10*3/2*4/3*...*11/10

=1/10*11/2

=11/20

Bạn cho mình đề bài

đúng rồi

Số?

\(=\frac{25}{35}\times\frac{18}{12}\times\frac{63}{24}\)

\(=\frac{5}{7}\times\frac{3}{2}\times\frac{21}{8}\)

\(=\frac{5\times3\times3}{1\times2\times8}\)

\(=\frac{45}{16}\)

jjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjj

25 / 12 * 18/35 * 63/24 

(((25/12*18)/35)*63)/24

= 2.8125

mk nhanh nhat