25 x 5 x 4 x 27 x 2 = 27000

25 . 5 . 4 . 27 . 2

= ( 25 . 4 ) . ( 5 . 2 ) . 27

=    100  .  10 .   27

=       1000    .    27

=          27 000

\(\frac{9}{10}-\frac{1}{90}-\frac{1}{72}-...-\frac{1}{6}-\frac{1}{2}\)

\(=\frac{9}{10}-\left(\frac{1}{2}+\frac{1}{6}+...+\frac{1}{72}+\frac{1}{90}\right)\)

\(=\frac{9}{10}-\left(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{8.9}+\frac{1}{9.10}\right)\)

\(=\frac{9}{10}-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)

\(=\frac{9}{10}-\left(1-\frac{1}{10}\right)\)

\(=\frac{9}{10}-\frac{9}{10}=0\)

Bang  0

 \(\frac{21}{11}\times\frac{22}{17}\times\frac{68}{63}\)

=\(\frac{21}{1}\times\frac{2}{17}\times\frac{68}{63}\)

= 21 x \(\frac{8}{63}\)

=\(\frac{8}{3}\)

a, 72 * 9 * 99 + 72 + 0,9

= 72 * (9 * 99 + 0,9)

= 72 * 891,9

= 64216,8

\(\frac{16}{27}>\frac{15}{29}\)

Kick mik nha , mik kick lại !!!!!!!!!!!!!!!!!!!!!!~-~

Do \(\frac{16}{27}>\frac{16}{29}>\frac{15}{29}\)

=> 16/27 > 15/29

Cách so sánh là tìm phân số ỡ giữa (phân số trung gian)

Ủng hộ mk nha ^_-

1 + 2 + 3 + ...........+x = 45

(x + 1){( x-1) :1 +1) :2 = 45

(x+1)x = 90 = 9 x10

x = 9