(1+x ) +( 3+x )+(5+x )+(7+x) +....+(97+x)+(99+x)=7050

(x+x+...+x) + ( 1+ 3 +...+ 97+99) = 7050

x.50 + 2500 = 7050

x.50 = 7050 - 2500= 4550

x=4550:50 = 91

Vậy x=91

( 1 + x ) + ( 3 + x ) + ( 5 + x ) + ... + ( 99 + x )   = 7050

(x + x + x + ... + x ) + ( 1 + 3 + 5 + ... + 99 )      = 7050

( x . 50 ) + ( 1 + 99 ) . 50 : 2                              = 7050

( x . 50  ) + 2500                                               = 7050

x . 50                                                                 = 7050 - 2500

x . 50                                                                 = 4550

x                                                                        = 4550 : 50

x                                                                        = 91

Vậy x = 91

học tốt!!!

ta có

dãy số lẻ từ 1 đến 99 có 50 số hạng

=>có 50 số x

=>(x+1)+(x+3)+....+(x+99)=4900

<=>50xX+(1+3.+...+99)=4900

=>50xX +(99+1)50/2=4900

=>50xX+2500=4900

=>50xX=4900-2500=2400

=>x=2400:50=48

vậy x=48

a) 1+2+3+....+ x = 1275 ( vế trái có x số hạng )

( 1 +x ) . x : 2 = 1275

( 1 + x ) . x = 1275 x 2 

( 1 + x ) . x = 2550

Vì 2550 = 50 x 51 => x = 50

Còn bài b) nữa bạn nhé!

không biết giải

2001 

____

1991

x : 3 - (1 x 49) + 99 = 127127

x : 3 = 127127 + 49 - 99

x : 3 = 127077

x = 127077 : 3

x =  42359

a: \(\left(1-\frac12\right)\times\left(1-\frac13\right)\times\ldots\times\left(1-\frac{1}{99}\right)\)

\(=\frac12\times\frac23\times\ldots\times\frac{98}{99}\)

\(=\frac{1}{99}\)

b: \(\left(x+\frac12\right)+\left(x+\frac16\right)+\left(x+\frac{1}{12}\right)+\left(x+\frac{1}{20}\right)+\cdots+\left(x+\frac{1}{90}\right)=\frac{99}{10}\)

=>\(\left(x+\frac{1}{1\times2}\right)+\left(x+\frac{1}{2\times3}\right)+\cdots+\left(x+\frac{1}{9\times10}\right)=\frac{99}{10}\)

=>\(9\times x+1-\frac12+\frac12-\frac13+\cdots+\frac19-\frac{1}{10}=\frac{99}{10}\)

=>\(9\times x+1-\frac{1}{10}=\frac{99}{10}\)

=>\(9\times x=\frac{99}{10}+\frac{1}{10}-1=\frac{100}{10}-1=10-1=9\)

=>x=1

\(\left(\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right).y=\frac{2}{3}\)

\(\frac{1}{2}.\left(1-\frac{1}{3}\right)+\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{5}\right)+\frac{1}{2}.\left(\frac{1}{5}-\frac{1}{7}\right)+\frac{1}{2}.\left(\frac{1}{7}-\frac{1}{9}\right)+\frac{1}{2}.\left(\frac{1}{9}-\frac{1}{11}\right).y=\frac{2}{3}\)

\(\frac{1}{2}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\right).y=\frac{2}{3}\)

\(\frac{1}{2}.\left(1-\frac{1}{11}\right).y=\frac{2}{3}\)

\(\left(1-\frac{1}{11}\right).y=\frac{4}{3}\)

\(\frac{10}{11}.y=\frac{4}{3}\)

\(\Rightarrow y=\frac{22}{15}\)

1+2+3+4+5+6+7+8+9+...........+99=X+1+2+3+4+5+6+7+8+9+.................+99

4950=4950+X

X=4950-4950

X=0

bằng 0 nha bn