18?

190:))

190?

khó thế toy ko bt =)))

toy cũng vậy

\(\dfrac{1}{7}\times\dfrac{21}{8}-\dfrac{3}{8}\times\dfrac{1}{7}-\dfrac{1}{7}\times\dfrac{2}{8}\\ =\dfrac{1}{7}\times\left(\dfrac{21}{8}-\dfrac{3}{8}-\dfrac{2}{8}\right)\\ =\dfrac{1}{7}\times\dfrac{16}{8}\\ =\dfrac{1}{7}\times2\\ =\dfrac{2}{7}\)

\(\dfrac{1}{7}\times\dfrac{21}{8}-\dfrac{3}{8}\times\dfrac{1}{7}-\dfrac{1}{7}\times\dfrac{2}{8}\)

=\(\dfrac{1}{7}\times\left(\dfrac{21}{8}-\dfrac{3}{8}-\dfrac{2}{8}\right)\)

=\(\dfrac{1}{7}\times2\)

=\(\dfrac{2}{7}\)

\(=\dfrac{1}{7}\text{×}\left(\dfrac{21}{8}-\dfrac{3}{8}-\dfrac{2}{8}\right)\)

\(=\dfrac{1}{7}\text{×}2\)

\(=\dfrac{2}{7}\)

1 + 4 + 7 + 10 + 13 + 16 + 19 = 70

34 + 77 - 66 + 13 = 58

\(1+4+7+10+13+16+19=\left(1+19\right)+\left(4+16\right)+\left(7+13\right)+10=20+20+20+10=70\)

\(34+77-66+13=58\)

58

0.13427871148

\(\dfrac{1}{3}\left(\dfrac{2}{7}+\dfrac{4}{7}+\dfrac{1}{7}\right)=\dfrac{1}{3}\times1=\dfrac{1}{3}\)

1/3

Đặt A=1x3+3x5+5x7+7x9+...+99x101

6A=6x(1x3+3x5+5x7+7x9+...+99x101)

6A=1x3x6+3x5x6+5x7x6+7x9x6+...+99x101x6

6A=1x3x(5+1)+3x5x(7-1)+5x7x(9-3)+7x9x(11-5)+...+99x101x(103-97)

6A=1x3x5+1x3+3x5x7-3x5+5x7x9-3x5x7+7x9x11-5x7x9+...+99x101x103-99x101x97

6A=3+99x101x103

=>A=\(\frac{\text{3+99x101x103}}{6}\)

bài đó có ở trong sách toán ko hay tự đố ở ngoài vậy?

ds:6

2:

=1-1+1-1=0

3:

a: =>34*(100+1)/2:a=17

=>a=101

b: =>5/3(x-1/2)=5/4

=>x-1/2=5/4:5/3=3/4

=>x=5/4

1a, \(\dfrac{2005}{2001}\) = 1+\(\dfrac{4}{2001}\); \(\dfrac{2009}{2005}\)=1+\(\dfrac{4}{2005}\)vì\(\dfrac{4}{2001}\)>\(\dfrac{4}{2005}\)nên\(\dfrac{2005}{2001}\)>\(\dfrac{2009}{2005}\)

1b,\(\dfrac{1313}{1515}\)=\(\dfrac{1313:101}{1515:101}\)= \(\dfrac{13}{15}\); \(\dfrac{131313}{151515}\)=\(\dfrac{131313:10101}{151515:10101}\)=\(\dfrac{13}{15}\)

Vậy \(\dfrac{13}{15}\)=\(\dfrac{1313}{1515}\)=\(\dfrac{131313}{151515}\)

\(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}\)

\(=\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+\dfrac{1}{4\cdot5}+\dfrac{1}{5\cdot6}+\dfrac{1}{6\cdot7}\)

\(=\dfrac{1}{1}\cdot\dfrac{1}{2}+\dfrac{1}{2}\cdot\dfrac{1}{3}+\dfrac{1}{3}\cdot\dfrac{1}{4}+\dfrac{1}{4}\cdot\dfrac{1}{5}+\dfrac{1}{5}\cdot\dfrac{1}{6}+\dfrac{1}{6}\cdot\dfrac{1}{7}\)

\(=\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}\)

\(=\dfrac{1}{1}-\dfrac{1}{7}=\dfrac{7}{7}-\dfrac{1}{7}=\dfrac{6}{7}\)

Khoảng cách giữa các số là 1 

Số số hạng là :

( 100 000 - 1 ) : 1 + 1 = 100 000 ( số )

Tổng trên bằng :

( 100 000 + 1 ) x 100 000 : 2 = 50005000

                                                 Đáp số : 5000 5000

À bấm thừa 1 số 0

Số các số hạng là:

(100000-1):1+1=100000 (số)

Tổng trên là:

(1+100000).100000:2=5000050000

Số số hạng của dãy là:

(100000 - 1) : 1+1=100000 số hạng

Tổng dãy trên là:

(1+100000) x100000:2=50000500000

đúng mình nha