(x+1)+(x+2)+...+(x+98)+(x+99)=9900

x+x+x+x+...x+(1+2+...+98+99)=9900

50x+2500=9900

=>50x=7400

vậy x=148

Tự làm đi

x + 1 + x + 2 + ... + x + 98 + x + 99 = 9900

( x + x + ... + x ) + ( 1 + 2 + ... + 98 + 99 ) = 9900

Số số hạng là : ( 99 - 1 ) : 1 + 1 = 99 ( số )

Tổng là : ( 99 + 1 ) x 99 : 2 = 4950

99x + 4950 = 9900

99x = 4950

x = 50

Vậy,......

a ) 37 x 27 + 63 x 27 

= ( 37 + 63 ) x 27

= 100 x 27

= 2700

b ) 1 + 2 + 3 + 4 + ... + 97 + 98 + 99

= ( 99 - 1 ) : 1 + 1 

= 99 x ( 99 + 1 ) : 2 

= 4950

c ) 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10

= ( 1 + 9 ) + ( 2 + 8 ) + ( 3 + 7 ) + ( 4 + 6 ) + ( 5 + 10 )

= 10 + 10 + 10 + 10 + 15

= 55

37 x 27 x 63 x27

=(37+63)x27

=100 x 27

\(\left(x+1\right)+\left(x+2\right)+...+\left(x+99\right)=9900\)

\(\Leftrightarrow99x+\left(\frac{99-1}{1}+1\right)=9900\)

\(\Leftrightarrow99x=9900-99\)

\(\Leftrightarrow x=99\)

k mk nha

(x + 1) +( x + 2) + ... + (x + 99 )= 9900

=>99x +(99-1/1  + 1 )=9900

=>99x=9900-99

=>x=90

ấn chậm quá

@@

Tui ko bít 

S=330000

Bạn giải ra cụ thể đc ko

A = 1x2 + 2x3 + 3x4 + 4x5 + ...+ 99x100

A x 3 = 1x2x3 + 2x3x3 + 3x4x3 + 4x5x3 + ... + 99x100x3

A x 3 = 1x2x3 + 2x3x(4-1) + 3x4x(5-2) + 4x5x(6-3) + ... + 99x100x(101-98) 

A x 3 = 1x2x3 + 2x3x4 - 1x2x3 + 3x4x5 - 2x3x4 + 4x5x6 - 3x4x5 + ... + 99x100x101 - 98x99x100.

A x 3 = 99x100x101 A = 99x100x101 : 3 A = 333300                                          tích cho mình với, ko chat àh

khó thế 

(1-2+3-4+.....-98+99)x(2013x6-2013-2013x5)

=(1-2+3-4+....-98+99)x[ 2013x(6-1-5)]

= (1-2+3-4+....-98+99)x(2013x0)

= (1-2+3-4+....-98+99)x0 = 0

= 1/1x2 + 1/2x3 + 1/3x4 ...... +1/9x10

= 1-1/2+1/2-1/3+1/3-1/4+........+1/9-1/10

=1-1/10=9/10

đặt A=1/1 x 1/2 + 1/2 x 1/3 + 1/3 + 1/4 + .......... + 1/9 x 1/10

\(A=\frac{1}{1}\cdot\frac{1}{2}+\frac{1}{2}\cdot\frac{1}{3}+...+\frac{1}{9}\cdot\frac{1}{10}\)

\(=\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{9.10}\)

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

\(=1-\frac{1}{10}\)

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

đặt B=2/1 x 2 + 2/2 x 3 + 2/3 x4 + .............. + 2/98 x 99 + 2/99 x 100

\(B=2\left(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{99.100}\right)\)

\(=2\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}\right)\)

\(=2\left(1-\frac{1}{100}\right)\)

\(=2\times\frac{99}{100}\)

\(=\frac{99}{50}\)