A = \(\dfrac{1}{1\times2}\) + \(\dfrac{3}{2\times5}\) + \(\dfrac{5}{5\times10}\) + \(\dfrac{4}{10\times14}\) + \(\dfrac{6}{14\times20}\)

A = \(\dfrac{1}{1}\) - \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) - \(\dfrac{1}{5}\) + \(\dfrac{1}{5}\) - \(\dfrac{1}{10}\) + \(\dfrac{1}{10}\) - \(\dfrac{1}{14}\) + \(\dfrac{1}{14}\) - \(\dfrac{1}{20}\)

A = \(\dfrac{1}{1}\) - \(\dfrac{1}{20}\)

A = \(\dfrac{19}{20}\)

`B = x^15 - 8x^14 + 8x^13 - 8x^122 + ... - 8x^2 + 8x - 5`

`B = x^15 - 7x^14 -x^14+7x^13+x^13-7x^12-...-x^2+7x+x-5`

`B = x^14(x-7) - x^14(x-7) +...+x^2(x-7)-x(x-7)+x-5`

`B = 7-5=2`

x=7 nên x+1=8

\(B=x^{15}-x^{14}\left(x+1\right)+x^{13}\left(x+1\right)-x^{12}\left(x+1\right)+...-x^2\left(x+1\right)+x\left(x+1\right)-5\)

\(=x^{15}-x^{15}-x^{14}+x^{14}-x^{13}+x^{13}-...-x^3-x^2+x^2+x+5\)

=x+5

=7+5

=12

ghi lại đề tý

\(B=x^{15}-8x^{14}+8x^{13}-8x^2+...-8x^2+8x-5\)

=> \(B=x^{15}-\left(x+1\right)x^{14}+\left(x+1\right)x^{13}-\left(x+1\right)x^{12}+...+\left(x+1\right)x-x+2\)

=>\(B=x^{15}-x^{15}+x^{14}-x^{14}+x^{13}-x^{13}-x^{12}+...+x^2+x-x+2\\\)

=>B=2

ai giúp mik với ak mik cần gấp

\(\dfrac{1}{1.4}+\dfrac{1}{4.2}+\dfrac{1}{2.8}+\dfrac{1}{8.4}+\dfrac{1}{4.16}+\dfrac{1}{16.8}\)

= \(\dfrac{1}{4}.\left(1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}\right)\)

= \(\dfrac{1}{4}.\left(\dfrac{3}{2}+\dfrac{3}{8}+\dfrac{3}{32}\right)\)

= \(\dfrac{1}{4}.\dfrac{3}{2}\left(1+\dfrac{1}{4}+\dfrac{1}{16}\right)\)

= \(\dfrac{1}{4}.\dfrac{3}{2}\left(\dfrac{16}{16}+\dfrac{4}{16}+\dfrac{1}{16}\right)\)

= \(\dfrac{3}{8}.\dfrac{21}{16}\)

= \(\dfrac{63}{128}\)

16

2 x 8 = 16

Chúc bạn học tốt.

😁😁😁

??????

`1/4 +x=5/2xx8/7`

`=> 1/4 + x= 40/14`

`=> 1/4 + x= 20/7`

`=> x= 20/7-1/4`

`=>x=73/28`

1/4 + x = 20/7

x = 20/7 - 1/4 

x = 73/28 

vậy x = 73/28

1/4 + x = 5/2 x 8/7      1,4 + x = 20/7          x = 20/7 - 1/4           x = 73/28

3+2+2+2.8-1+4.1

=3+2+2+16-1+4

=(3+2+2-1)+(16+4)

=(5+2-1)+20

=(7-1)+20

=6+20

=26