\(46\cdot99\)

\(=46\cdot\left(100-1\right)\)

\(=46\cdot100-46\)

\(=4600-46\)

\(=4554\)

___________

\(34\cdot11\)

\(=34\cdot\left(10+1\right)\)

\(=34\cdot10+34\)

\(=340+34\)

\(=374\)

___________

\(25\cdot12\) 

\(=5\cdot5\cdot12\)

\(=5\cdot60\)

\(=300\)

__________

\(15\cdot4\)

\(=15\cdot2\cdot2\)

\(=30\cdot2\)

\(=60\)

____________

\(45\cdot6\)

\(=45\cdot2\cdot3\)

\(=90\cdot3\)

\(=2700\)

________

\(13\cdot99\)

\(=13\cdot\left(100-1\right)\)

\(=13\cdot100-13\)

\(=1300-13\)

\(=1287\)

______________

\(16\cdot19\)

\(=16\cdot\left(20-1\right)\)

\(=16\cdot20-16\)

\(=320-16\)

\(=304\)

_____________

\(35\cdot98\)

\(=35\cdot\left(100-2\right)\)

\(=35\cdot100-35\cdot2\)

\(=3500-70\)

\(=3430\)

____________

\(125\cdot16\)

\(=125\cdot8\cdot2\)

\(=1000\cdot2\)

\(=2000\)

___________

\(47\cdot101\)

\(=47\cdot\left(100+1\right)\)

\(=47\cdot100+47\)

\(=4700+47\)

\(=4747\)

46 x 99 =4554  , 34 x 11 = 374 , 25 x 12 =- 300 , 15 x 4 = 60 , 45 x 6 = 270 , 13 x 99 = 1287 , 16 x 19 = 304

35 x 98 = 3430 , 125 x 16  = 2000 ,  47 x 101  = 4747

a: \(\left(-34\right)\cdot11\)

\(=-34\left(10+1\right)\)

\(=-34\cdot10-34\cdot1=-340-34=-374\)

b: \(250\cdot\left(-21\right)\)

\(=-250\left(20+1\right)\)

\(=-250\cdot20-250\cdot1=-5000-250=-5250\)

c: \(\left(-23\right)\cdot101\)

\(=\left(-23\right)\left(100+1\right)\)

\(=-23\cdot100-23\cdot1=-2300-23=-2323\)

d: \(31\cdot\left(-99\right)=-31\cdot99\)

\(=-31\left(100-1\right)\)

\(=-31\cdot100+31\cdot1\)

=-3100+31

=-3069

a)=-374                   b)=-5250

c)=-2323                  d)=-3069

?? .......fmdnfhxvfvhzyv fhddddgnfhgmjvhnjghytdthtanththnghng nhng 

\(\frac{1}{5.8}\)+\(\frac{1}{8.11}\)+\(\frac{1}{11.14}\)+........+\(\frac{1}{x.\left(x+3\right)}\)=\(\frac{101}{1540}\)

3(.\(\frac{1}{5.8}+\frac{1}{8.11}\)+\(\frac{1}{11.14}+.......+\frac{1}{x.\left(x+3\right)}=\frac{101}{1540}.3=\frac{303}{1540}\)

\(\frac{3}{5.8}+\frac{3}{8.11}+\frac{3}{11.14}+.....+\frac{3}{x\left(x+3\right)}=\frac{303}{1540}\)

\(\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+....+\frac{1}{x}-\frac{1}{x+3}=\frac{303}{1540}\)

\(\frac{1}{5}-\frac{1}{x+3}=\frac{303}{1540}\)

\(\frac{1}{x+3}=\frac{1}{5}-\frac{303}{1540}=\frac{1}{308}\)

=>\(x+3=308\)

\(x=308-3=305\)

Vậy \(x=305\)

\(\frac{1}{5.8}+\frac{1}{8.11}+...+\frac{1}{x\left(x+3\right)}=\frac{101}{1540}\)

=> \(\frac{1}{3}\left(\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{x}-\frac{1}{x+3}\right)=\frac{101}{1540}\)

=> \(\frac{1}{5}-\frac{1}{x+3}=\frac{101}{1540}:\frac{1}{3}\)

=> \(\frac{1}{5}-\frac{1}{x+3}=\frac{303}{1540}\)

=> \(\frac{1}{x+3}=\frac{1}{5}-\frac{303}{1540}\)

=> \(\frac{1}{x+3}=\frac{1}{308}\)

=> x + 3 = 308

     x = 308 - 5

     x = 303

Pikachu đơn giản thì làm thử đừng nói mà ko làm nha ^_^

duyệt đi

Đơn giản -_-