\(P=\frac{1}{99}-\left(\frac{1}{1.2}+\frac{1}{2.3}+....+\frac{1}{98.99}\right)\)

\(=\frac{1}{99}-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{98}-\frac{1}{99}\right)\)

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

\(=\frac{1}{99}-\frac{98}{99}\)

\(=-\frac{97}{99}\)

Vậy \(P=-\frac{97}{99}\)

P=-1/1.2-1/2.3-...-1/98.99-1/99

P=-(1/1.2+1/2.3+...+1/98.99+1/99)

P=-1

bằng 13 k nhé

1x13=13

13 nhé bn

Tk mình nhé! 

ko bt làm thì có :))

mau lên ik dễ mà                               

1/

a)19/20

b)(1/4+4/9):(3/2-2/3)^2

=25/36:25/36

=1

2/

a) =>x.4=2.-3

=>x.4=-6

=>x=-1,5

b) =>1/6x=5/3+1/4

=>1/6x=23/12

=>x=11,5

bit lm rùi thì đăng lm j nữa ko ai rảnh mà đi lm

bài toán này không hợp lệ bạn ơi có 2 dấu + liên tiếp

1+1+1+1+1+1+1+1+1+1+1+1+1++1+11+1+11+1+1+11+1+1+1+1+1=52

=1.22+11.3

=22+33

=55

S=1/5=(1/13+1/14+1/15)+(1/61+1/62+1/63)

suy ra S<1/5+1/12x3+1/60x3

S<1/5+1/4+1/20

=>S<1/2

Xét tử số:

A = 1 + 1/3 + 1/5 + ... + 1/99

A = (1 + 1/99) + (1/3 + 1/97) +...+ (1/49 + 1/51)

A = (99/99*1 + 1/99*1) + (97/3*97 + 3/97*3) +...+ (51/49*51 + 49/51*49)

A = 100/1*99 + 100/3*97 +...+ 100/49*51

A = 100*(1/1*99 + 1/3*97 +...+ 1/49*51)

Xét mẫu số:

B = 1/1*99 + 1/ 3*97 +.....+1/99*1

B = 2/1*99 + 2/3*97 +...+ 2/49*51

B = 2*(1/1*99 + 1/3*97 +...+ 1/49*51)

=> A/B = 100*(1/1*99 + 1/3*97 +...+ 1/49*51) / 2*(1/1*99 + 1/3*97 +...+ 1/49*51)

=> A/B = 100/2 = 50

Hiu hiu, khó quá

`1/2 xx 1/3 xx 1/4`

`= (1xx1xx1)/(2xx3xx4)`

`= 1/24`

__

`1/2 xx 1/3 : 1/4`

`= 1/2 xx 1/3 xx 4`

`= (1xx1xx4)/(2xx3)`

`= 4/6`

`=2/3`

__

`1/2 : 1/3 xx1/4`

`= 1/2 xx 3 xx 1/4`

`=(1xx3xx1)/(2xx4)`

`= 3/8`

__

`1/2 : 1/3 : 1/4`

`= 1/2 xx 3xx4`

`= 12/2`

`=6`

`1/2xx1/3xx1/4`

`=1/24`

`1/2xx1/3:1/4`

`=1/6xx4`

`=4/6=2/3`

`1/2:1/3xx1/4`

`=1/2xx3xx1/4`

`=3/2xx1/4`

`=3/8`

`1/2:1/3:1/4`

`=1/2xx3xx4`

`=6`

=6