bang 0

\(-1999.19981998+19991999.1998\)

\(=-1999.\left(19980000+1998\right)+1998.\left(19990000+1999\right)\)

\(=-1999.19980000-1999.1998+1998.19990000+1998.1999\)

\(=\left(1998.1999-1999.1998\right)+\left(1998.19990000-1999.19980000\right)\)

\(=\left(1998.1999-1999.1998\right)+10000\left(1998.1999-1999.1998\right)=0\)

( 1999 x 1998 + 1998 + 1997 ) + ( 1 + 1/2 / 11/2 - 11/3 )

= [ 1998( 1999 + 1 ) + 1997 ] + ( 3/2 / 11/6 )

= ( 1998 x 2000 + 1997 ) + ( 3/2 . 6/11 ) 

= 3997997 + 9/11

= 3997997,818

A=-34979 nha ban k cho mk 

=-1999.1998.10 001+1999.10 001.1998

=(-1999+1999).1998.10 001

=0.1998.10 001=0

-1999.19981998+19991999.1998

=-1999.1998.10001+1999.10001.1998

=1998.10001(-1999+1999)

=1998.10001.0

=0 

\(C=\frac{5}{1.3}+\frac{5}{3.5}+\frac{5}{5.7}+...+\frac{5}{997.999}\)

\(\Leftrightarrow C=\frac{5}{2}\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{997.999}\right)\)

\(\Leftrightarrow C=\frac{5}{2}\left(\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{997}-\frac{1}{999}\right)\)

\(\Leftrightarrow C=\frac{5}{2}\left(1-\frac{1}{999}\right)=\frac{5}{2}.\frac{998}{999}=\frac{2495}{999}=2\frac{497}{999}\)

\(A=\frac{2}{4}+\frac{2}{28}+\frac{2}{70}+\frac{2}{130}+\frac{2}{208}\)

\(\Leftrightarrow A=\frac{2}{1.4}+\frac{2}{4.7}+\frac{2}{7.10}+\frac{2}{10.13}+\frac{2}{13.16}\)

\(\Leftrightarrow A=\frac{2}{3}\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+\frac{3}{13.16}\right)\)

\(\Leftrightarrow A=\frac{2}{3}\left(\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}\right)\)

\(\Leftrightarrow A=\frac{2}{3}\left(1-\frac{1}{16}\right)=\frac{2}{3}.\frac{15}{16}=\frac{5}{8}\)

C = 5/1x3 + 5/3x5 + 5/5x7 + ... + 5/997x999

C = 5 - 5/3 + 5/3 - 5/5 + 5/5 - 5/7 + ... + 5/997 - 5/999

C = 5 - 5/999

C = bạn tự tính nhé !

A = 2/4 + 2/28 + 2/70 + 2/130 + 2/208

A = 2/1x4 + 2/4x7 + 2/7x10 + 2/10x13 + 2/13x16

A = 2 - 2/4 + 2/4 - 2/7 + 2/7 - 2/10 + 2/10 - 2/13 + 2/13 - 2/16

A = 2 - 2/16

A = bạn tự tính nhé !

\(\frac{2C}{5}=\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+..+\frac{2}{97.99}\)

\(\frac{2C}{5}=\frac{3-1}{1.3}+\frac{5-3}{3.5}+\frac{7-5}{5.7}+...+\frac{99-97}{97.99}\)

\(\frac{2C}{5}=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{99}\)

\(\frac{2C}{5}=1-\frac{1}{99}=\frac{98}{99}\Rightarrow C=\frac{98.5}{99.2}=\frac{245}{99}\)

\(\frac{3A}{2}=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+\frac{3}{13.16}\)

\(\frac{3A}{2}=\frac{4-1}{1.4}+\frac{7-4}{4.7}+\frac{10-7}{7.10}+\frac{13-10}{10.13}+\frac{16-13}{13.16}\)

\(\frac{3A}{2}=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}\)

\(\frac{3A}{2}=1-\frac{1}{16}=\frac{15}{16}\Rightarrow A=\frac{15.2}{16.3}=\frac{5}{8}\)

cho mik 1 lik-e nha Nguyễn Hoàng Thiên Hương

12000 - ( 1500 . 2 + 1800 . 3 + 1800 . 2 : 3 ) 

= 12000 - ( 3000 + 5400 + 3600 : 3 )

= 12000 - ( 3000 + 5400 + 1200 ) 

= 12000 - 9600

= 2400

12 000 - (1500 . 2 + 1800 . 3 + 1800 . 2 : 3) 

=12 000 - (3000 + 5400 + 3600 : 3)

= 12 000 - (3000 + 5400 + 1200)

= 12 000 - 9600 = 2400

= 12 000 -(3000 + 5400 + 1200) = 12 000 - 9600 = 2400

A=3+6+9+12+...+2007

A=\(\frac{\left(3+2007\right).699}{2}\)

A=702495

\(B=2.52.12+4.6.87-3.8.40\)

\(B=24.53+24.87-24.40\)

\(B=24\left(53+87-40\right)\)

\(B=24.100\)

\(B=2400\)